602 lines
15 KiB
Go
602 lines
15 KiB
Go
// Copyright 2010 The Freetype-Go Authors. All rights reserved.
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// Use of this source code is governed by your choice of either the
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// FreeType License or the GNU General Public License version 2 (or
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// any later version), both of which can be found in the LICENSE file.
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// Package raster provides an anti-aliasing 2-D rasterizer.
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//
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// It is part of the larger Freetype suite of font-related packages, but the
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// raster package is not specific to font rasterization, and can be used
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// standalone without any other Freetype package.
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//
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// Rasterization is done by the same area/coverage accumulation algorithm as
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// the Freetype "smooth" module, and the Anti-Grain Geometry library. A
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// description of the area/coverage algorithm is at
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// http://projects.tuxee.net/cl-vectors/section-the-cl-aa-algorithm
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package raster // import "github.com/golang/freetype/raster"
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import (
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"strconv"
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"golang.org/x/image/math/fixed"
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)
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// A cell is part of a linked list (for a given yi co-ordinate) of accumulated
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// area/coverage for the pixel at (xi, yi).
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type cell struct {
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xi int
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area, cover int
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next int
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}
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type Rasterizer struct {
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// If false, the default behavior is to use the even-odd winding fill
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// rule during Rasterize.
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UseNonZeroWinding bool
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// An offset (in pixels) to the painted spans.
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Dx, Dy int
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// The width of the Rasterizer. The height is implicit in len(cellIndex).
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width int
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// splitScaleN is the scaling factor used to determine how many times
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// to decompose a quadratic or cubic segment into a linear approximation.
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splitScale2, splitScale3 int
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// The current pen position.
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a fixed.Point26_6
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// The current cell and its area/coverage being accumulated.
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xi, yi int
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area, cover int
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// Saved cells.
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cell []cell
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// Linked list of cells, one per row.
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cellIndex []int
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// Buffers.
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cellBuf [256]cell
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cellIndexBuf [64]int
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spanBuf [64]Span
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}
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// findCell returns the index in r.cell for the cell corresponding to
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// (r.xi, r.yi). The cell is created if necessary.
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func (r *Rasterizer) findCell() int {
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if r.yi < 0 || r.yi >= len(r.cellIndex) {
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return -1
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}
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xi := r.xi
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if xi < 0 {
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xi = -1
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} else if xi > r.width {
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xi = r.width
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}
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i, prev := r.cellIndex[r.yi], -1
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for i != -1 && r.cell[i].xi <= xi {
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if r.cell[i].xi == xi {
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return i
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}
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i, prev = r.cell[i].next, i
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}
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c := len(r.cell)
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if c == cap(r.cell) {
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buf := make([]cell, c, 4*c)
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copy(buf, r.cell)
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r.cell = buf[0 : c+1]
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} else {
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r.cell = r.cell[0 : c+1]
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}
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r.cell[c] = cell{xi, 0, 0, i}
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if prev == -1 {
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r.cellIndex[r.yi] = c
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} else {
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r.cell[prev].next = c
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}
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return c
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}
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// saveCell saves any accumulated r.area/r.cover for (r.xi, r.yi).
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func (r *Rasterizer) saveCell() {
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if r.area != 0 || r.cover != 0 {
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i := r.findCell()
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if i != -1 {
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r.cell[i].area += r.area
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r.cell[i].cover += r.cover
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}
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r.area = 0
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r.cover = 0
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}
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}
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// setCell sets the (xi, yi) cell that r is accumulating area/coverage for.
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func (r *Rasterizer) setCell(xi, yi int) {
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if r.xi != xi || r.yi != yi {
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r.saveCell()
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r.xi, r.yi = xi, yi
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}
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}
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// scan accumulates area/coverage for the yi'th scanline, going from
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// x0 to x1 in the horizontal direction (in 26.6 fixed point co-ordinates)
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// and from y0f to y1f fractional vertical units within that scanline.
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func (r *Rasterizer) scan(yi int, x0, y0f, x1, y1f fixed.Int26_6) {
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// Break the 26.6 fixed point X co-ordinates into integral and fractional parts.
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x0i := int(x0) / 64
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x0f := x0 - fixed.Int26_6(64*x0i)
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x1i := int(x1) / 64
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x1f := x1 - fixed.Int26_6(64*x1i)
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// A perfectly horizontal scan.
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if y0f == y1f {
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r.setCell(x1i, yi)
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return
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}
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dx, dy := x1-x0, y1f-y0f
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// A single cell scan.
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if x0i == x1i {
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r.area += int((x0f + x1f) * dy)
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r.cover += int(dy)
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return
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}
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// There are at least two cells. Apart from the first and last cells,
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// all intermediate cells go through the full width of the cell,
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// or 64 units in 26.6 fixed point format.
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var (
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p, q, edge0, edge1 fixed.Int26_6
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xiDelta int
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)
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if dx > 0 {
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p, q = (64-x0f)*dy, dx
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edge0, edge1, xiDelta = 0, 64, 1
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} else {
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p, q = x0f*dy, -dx
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edge0, edge1, xiDelta = 64, 0, -1
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}
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yDelta, yRem := p/q, p%q
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if yRem < 0 {
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yDelta -= 1
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yRem += q
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}
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// Do the first cell.
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xi, y := x0i, y0f
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r.area += int((x0f + edge1) * yDelta)
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r.cover += int(yDelta)
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xi, y = xi+xiDelta, y+yDelta
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r.setCell(xi, yi)
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if xi != x1i {
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// Do all the intermediate cells.
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p = 64 * (y1f - y + yDelta)
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fullDelta, fullRem := p/q, p%q
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if fullRem < 0 {
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fullDelta -= 1
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fullRem += q
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}
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yRem -= q
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for xi != x1i {
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yDelta = fullDelta
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yRem += fullRem
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if yRem >= 0 {
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yDelta += 1
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yRem -= q
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}
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r.area += int(64 * yDelta)
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r.cover += int(yDelta)
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xi, y = xi+xiDelta, y+yDelta
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r.setCell(xi, yi)
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}
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}
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// Do the last cell.
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yDelta = y1f - y
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r.area += int((edge0 + x1f) * yDelta)
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r.cover += int(yDelta)
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}
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// Start starts a new curve at the given point.
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func (r *Rasterizer) Start(a fixed.Point26_6) {
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r.setCell(int(a.X/64), int(a.Y/64))
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r.a = a
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}
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// Add1 adds a linear segment to the current curve.
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func (r *Rasterizer) Add1(b fixed.Point26_6) {
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x0, y0 := r.a.X, r.a.Y
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x1, y1 := b.X, b.Y
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dx, dy := x1-x0, y1-y0
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// Break the 26.6 fixed point Y co-ordinates into integral and fractional
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// parts.
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y0i := int(y0) / 64
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y0f := y0 - fixed.Int26_6(64*y0i)
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y1i := int(y1) / 64
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y1f := y1 - fixed.Int26_6(64*y1i)
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if y0i == y1i {
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// There is only one scanline.
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r.scan(y0i, x0, y0f, x1, y1f)
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} else if dx == 0 {
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// This is a vertical line segment. We avoid calling r.scan and instead
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// manipulate r.area and r.cover directly.
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var (
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edge0, edge1 fixed.Int26_6
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yiDelta int
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)
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if dy > 0 {
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edge0, edge1, yiDelta = 0, 64, 1
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} else {
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edge0, edge1, yiDelta = 64, 0, -1
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}
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x0i, yi := int(x0)/64, y0i
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x0fTimes2 := (int(x0) - (64 * x0i)) * 2
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// Do the first pixel.
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dcover := int(edge1 - y0f)
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darea := int(x0fTimes2 * dcover)
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r.area += darea
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r.cover += dcover
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yi += yiDelta
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r.setCell(x0i, yi)
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// Do all the intermediate pixels.
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dcover = int(edge1 - edge0)
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darea = int(x0fTimes2 * dcover)
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for yi != y1i {
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r.area += darea
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r.cover += dcover
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yi += yiDelta
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r.setCell(x0i, yi)
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}
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// Do the last pixel.
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dcover = int(y1f - edge0)
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darea = int(x0fTimes2 * dcover)
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r.area += darea
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r.cover += dcover
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} else {
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// There are at least two scanlines. Apart from the first and last
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// scanlines, all intermediate scanlines go through the full height of
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// the row, or 64 units in 26.6 fixed point format.
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var (
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p, q, edge0, edge1 fixed.Int26_6
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yiDelta int
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)
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if dy > 0 {
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p, q = (64-y0f)*dx, dy
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edge0, edge1, yiDelta = 0, 64, 1
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} else {
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p, q = y0f*dx, -dy
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edge0, edge1, yiDelta = 64, 0, -1
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}
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xDelta, xRem := p/q, p%q
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if xRem < 0 {
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xDelta -= 1
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xRem += q
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}
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// Do the first scanline.
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x, yi := x0, y0i
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r.scan(yi, x, y0f, x+xDelta, edge1)
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x, yi = x+xDelta, yi+yiDelta
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r.setCell(int(x)/64, yi)
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if yi != y1i {
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// Do all the intermediate scanlines.
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p = 64 * dx
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fullDelta, fullRem := p/q, p%q
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if fullRem < 0 {
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fullDelta -= 1
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fullRem += q
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}
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xRem -= q
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for yi != y1i {
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xDelta = fullDelta
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xRem += fullRem
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if xRem >= 0 {
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xDelta += 1
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xRem -= q
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}
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r.scan(yi, x, edge0, x+xDelta, edge1)
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x, yi = x+xDelta, yi+yiDelta
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r.setCell(int(x)/64, yi)
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}
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}
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// Do the last scanline.
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r.scan(yi, x, edge0, x1, y1f)
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}
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// The next lineTo starts from b.
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r.a = b
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}
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// Add2 adds a quadratic segment to the current curve.
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func (r *Rasterizer) Add2(b, c fixed.Point26_6) {
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// Calculate nSplit (the number of recursive decompositions) based on how
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// 'curvy' it is. Specifically, how much the middle point b deviates from
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// (a+c)/2.
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dev := maxAbs(r.a.X-2*b.X+c.X, r.a.Y-2*b.Y+c.Y) / fixed.Int26_6(r.splitScale2)
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nsplit := 0
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for dev > 0 {
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dev /= 4
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nsplit++
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}
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// dev is 32-bit, and nsplit++ every time we shift off 2 bits, so maxNsplit
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// is 16.
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const maxNsplit = 16
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if nsplit > maxNsplit {
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panic("freetype/raster: Add2 nsplit too large: " + strconv.Itoa(nsplit))
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}
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// Recursively decompose the curve nSplit levels deep.
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var (
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pStack [2*maxNsplit + 3]fixed.Point26_6
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sStack [maxNsplit + 1]int
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i int
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)
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sStack[0] = nsplit
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pStack[0] = c
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pStack[1] = b
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pStack[2] = r.a
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for i >= 0 {
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s := sStack[i]
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p := pStack[2*i:]
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if s > 0 {
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// Split the quadratic curve p[:3] into an equivalent set of two
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// shorter curves: p[:3] and p[2:5]. The new p[4] is the old p[2],
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// and p[0] is unchanged.
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mx := p[1].X
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p[4].X = p[2].X
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p[3].X = (p[4].X + mx) / 2
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p[1].X = (p[0].X + mx) / 2
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p[2].X = (p[1].X + p[3].X) / 2
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my := p[1].Y
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p[4].Y = p[2].Y
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p[3].Y = (p[4].Y + my) / 2
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p[1].Y = (p[0].Y + my) / 2
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p[2].Y = (p[1].Y + p[3].Y) / 2
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// The two shorter curves have one less split to do.
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sStack[i] = s - 1
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sStack[i+1] = s - 1
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i++
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} else {
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// Replace the level-0 quadratic with a two-linear-piece
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// approximation.
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midx := (p[0].X + 2*p[1].X + p[2].X) / 4
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midy := (p[0].Y + 2*p[1].Y + p[2].Y) / 4
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r.Add1(fixed.Point26_6{midx, midy})
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r.Add1(p[0])
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i--
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}
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}
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}
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// Add3 adds a cubic segment to the current curve.
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func (r *Rasterizer) Add3(b, c, d fixed.Point26_6) {
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// Calculate nSplit (the number of recursive decompositions) based on how
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// 'curvy' it is.
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dev2 := maxAbs(r.a.X-3*(b.X+c.X)+d.X, r.a.Y-3*(b.Y+c.Y)+d.Y) / fixed.Int26_6(r.splitScale2)
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dev3 := maxAbs(r.a.X-2*b.X+d.X, r.a.Y-2*b.Y+d.Y) / fixed.Int26_6(r.splitScale3)
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nsplit := 0
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for dev2 > 0 || dev3 > 0 {
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dev2 /= 8
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dev3 /= 4
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nsplit++
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}
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// devN is 32-bit, and nsplit++ every time we shift off 2 bits, so
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// maxNsplit is 16.
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const maxNsplit = 16
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if nsplit > maxNsplit {
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panic("freetype/raster: Add3 nsplit too large: " + strconv.Itoa(nsplit))
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}
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// Recursively decompose the curve nSplit levels deep.
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var (
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pStack [3*maxNsplit + 4]fixed.Point26_6
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sStack [maxNsplit + 1]int
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i int
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)
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sStack[0] = nsplit
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pStack[0] = d
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pStack[1] = c
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pStack[2] = b
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pStack[3] = r.a
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for i >= 0 {
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s := sStack[i]
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p := pStack[3*i:]
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if s > 0 {
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// Split the cubic curve p[:4] into an equivalent set of two
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// shorter curves: p[:4] and p[3:7]. The new p[6] is the old p[3],
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// and p[0] is unchanged.
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m01x := (p[0].X + p[1].X) / 2
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m12x := (p[1].X + p[2].X) / 2
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m23x := (p[2].X + p[3].X) / 2
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p[6].X = p[3].X
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p[5].X = m23x
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p[1].X = m01x
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p[2].X = (m01x + m12x) / 2
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p[4].X = (m12x + m23x) / 2
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p[3].X = (p[2].X + p[4].X) / 2
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m01y := (p[0].Y + p[1].Y) / 2
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m12y := (p[1].Y + p[2].Y) / 2
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m23y := (p[2].Y + p[3].Y) / 2
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p[6].Y = p[3].Y
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p[5].Y = m23y
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p[1].Y = m01y
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p[2].Y = (m01y + m12y) / 2
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p[4].Y = (m12y + m23y) / 2
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p[3].Y = (p[2].Y + p[4].Y) / 2
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// The two shorter curves have one less split to do.
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sStack[i] = s - 1
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sStack[i+1] = s - 1
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i++
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} else {
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// Replace the level-0 cubic with a two-linear-piece approximation.
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midx := (p[0].X + 3*(p[1].X+p[2].X) + p[3].X) / 8
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midy := (p[0].Y + 3*(p[1].Y+p[2].Y) + p[3].Y) / 8
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r.Add1(fixed.Point26_6{midx, midy})
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r.Add1(p[0])
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i--
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}
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}
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}
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// AddPath adds the given Path.
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func (r *Rasterizer) AddPath(p Path) {
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for i := 0; i < len(p); {
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switch p[i] {
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case 0:
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r.Start(
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fixed.Point26_6{p[i+1], p[i+2]},
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)
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i += 4
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case 1:
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r.Add1(
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fixed.Point26_6{p[i+1], p[i+2]},
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)
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i += 4
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case 2:
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r.Add2(
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fixed.Point26_6{p[i+1], p[i+2]},
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fixed.Point26_6{p[i+3], p[i+4]},
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)
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i += 6
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case 3:
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r.Add3(
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fixed.Point26_6{p[i+1], p[i+2]},
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fixed.Point26_6{p[i+3], p[i+4]},
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fixed.Point26_6{p[i+5], p[i+6]},
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)
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i += 8
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default:
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panic("freetype/raster: bad path")
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}
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}
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}
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// AddStroke adds a stroked Path.
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func (r *Rasterizer) AddStroke(q Path, width fixed.Int26_6, cr Capper, jr Joiner) {
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Stroke(r, q, width, cr, jr)
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}
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// areaToAlpha converts an area value to a uint32 alpha value. A completely
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// filled pixel corresponds to an area of 64*64*2, and an alpha of 0xffff. The
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// conversion of area values greater than this depends on the winding rule:
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|
// even-odd or non-zero.
|
|
func (r *Rasterizer) areaToAlpha(area int) uint32 {
|
|
// The C Freetype implementation (version 2.3.12) does "alpha := area>>1"
|
|
// without the +1. Round-to-nearest gives a more symmetric result than
|
|
// round-down. The C implementation also returns 8-bit alpha, not 16-bit
|
|
// alpha.
|
|
a := (area + 1) >> 1
|
|
if a < 0 {
|
|
a = -a
|
|
}
|
|
alpha := uint32(a)
|
|
if r.UseNonZeroWinding {
|
|
if alpha > 0x0fff {
|
|
alpha = 0x0fff
|
|
}
|
|
} else {
|
|
alpha &= 0x1fff
|
|
if alpha > 0x1000 {
|
|
alpha = 0x2000 - alpha
|
|
} else if alpha == 0x1000 {
|
|
alpha = 0x0fff
|
|
}
|
|
}
|
|
// alpha is now in the range [0x0000, 0x0fff]. Convert that 12-bit alpha to
|
|
// 16-bit alpha.
|
|
return alpha<<4 | alpha>>8
|
|
}
|
|
|
|
// Rasterize converts r's accumulated curves into Spans for p. The Spans passed
|
|
// to p are non-overlapping, and sorted by Y and then X. They all have non-zero
|
|
// width (and 0 <= X0 < X1 <= r.width) and non-zero A, except for the final
|
|
// Span, which has Y, X0, X1 and A all equal to zero.
|
|
func (r *Rasterizer) Rasterize(p Painter) {
|
|
r.saveCell()
|
|
s := 0
|
|
for yi := 0; yi < len(r.cellIndex); yi++ {
|
|
xi, cover := 0, 0
|
|
for c := r.cellIndex[yi]; c != -1; c = r.cell[c].next {
|
|
if cover != 0 && r.cell[c].xi > xi {
|
|
alpha := r.areaToAlpha(cover * 64 * 2)
|
|
if alpha != 0 {
|
|
xi0, xi1 := xi, r.cell[c].xi
|
|
if xi0 < 0 {
|
|
xi0 = 0
|
|
}
|
|
if xi1 >= r.width {
|
|
xi1 = r.width
|
|
}
|
|
if xi0 < xi1 {
|
|
r.spanBuf[s] = Span{yi + r.Dy, xi0 + r.Dx, xi1 + r.Dx, alpha}
|
|
s++
|
|
}
|
|
}
|
|
}
|
|
cover += r.cell[c].cover
|
|
alpha := r.areaToAlpha(cover*64*2 - r.cell[c].area)
|
|
xi = r.cell[c].xi + 1
|
|
if alpha != 0 {
|
|
xi0, xi1 := r.cell[c].xi, xi
|
|
if xi0 < 0 {
|
|
xi0 = 0
|
|
}
|
|
if xi1 >= r.width {
|
|
xi1 = r.width
|
|
}
|
|
if xi0 < xi1 {
|
|
r.spanBuf[s] = Span{yi + r.Dy, xi0 + r.Dx, xi1 + r.Dx, alpha}
|
|
s++
|
|
}
|
|
}
|
|
if s > len(r.spanBuf)-2 {
|
|
p.Paint(r.spanBuf[:s], false)
|
|
s = 0
|
|
}
|
|
}
|
|
}
|
|
p.Paint(r.spanBuf[:s], true)
|
|
}
|
|
|
|
// Clear cancels any previous calls to r.Start or r.AddXxx.
|
|
func (r *Rasterizer) Clear() {
|
|
r.a = fixed.Point26_6{}
|
|
r.xi = 0
|
|
r.yi = 0
|
|
r.area = 0
|
|
r.cover = 0
|
|
r.cell = r.cell[:0]
|
|
for i := 0; i < len(r.cellIndex); i++ {
|
|
r.cellIndex[i] = -1
|
|
}
|
|
}
|
|
|
|
// SetBounds sets the maximum width and height of the rasterized image and
|
|
// calls Clear. The width and height are in pixels, not fixed.Int26_6 units.
|
|
func (r *Rasterizer) SetBounds(width, height int) {
|
|
if width < 0 {
|
|
width = 0
|
|
}
|
|
if height < 0 {
|
|
height = 0
|
|
}
|
|
// Use the same ssN heuristic as the C Freetype (version 2.4.0)
|
|
// implementation.
|
|
ss2, ss3 := 32, 16
|
|
if width > 24 || height > 24 {
|
|
ss2, ss3 = 2*ss2, 2*ss3
|
|
if width > 120 || height > 120 {
|
|
ss2, ss3 = 2*ss2, 2*ss3
|
|
}
|
|
}
|
|
r.width = width
|
|
r.splitScale2 = ss2
|
|
r.splitScale3 = ss3
|
|
r.cell = r.cellBuf[:0]
|
|
if height > len(r.cellIndexBuf) {
|
|
r.cellIndex = make([]int, height)
|
|
} else {
|
|
r.cellIndex = r.cellIndexBuf[:height]
|
|
}
|
|
r.Clear()
|
|
}
|
|
|
|
// NewRasterizer creates a new Rasterizer with the given bounds.
|
|
func NewRasterizer(width, height int) *Rasterizer {
|
|
r := new(Rasterizer)
|
|
r.SetBounds(width, height)
|
|
return r
|
|
}
|