internal/scene: extract compute shader encoding to a separate package

We're about to encode clip.Paths with the format compatible with the
compute renderer. This change extracts the encoding to a re-usable
package.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

internal/scene/scene.go

@@ -0,0 +1,125 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+// Package scene encodes and decodes graphics commands in the format used by the
+// compute renderer.
+package scene
+
+import (
+	"image/color"
+	"math"
+
+	"gioui.org/f32"
+)
+
+type Command [sceneElemSize / 4]uint32
+
+const sceneElemSize = 36
+
+// GPU commands from scene.h
+const (
+	elemNop = iota
+	elemStrokeLine
+	elemFillLine
+	elemStrokeQuad
+	elemFillQuad
+	elemStrokeCubic
+	elemFillCubic
+	elemStroke
+	elemFill
+	elemLineWidth
+	elemTransform
+	elemBeginClip
+	elemEndClip
+	elemFillImage
+)
+
+func Line(start, end f32.Point, stroke bool, flags uint32) Command {
+	tag := uint32(elemFillLine)
+	if stroke {
+		tag = elemStrokeLine
+	}
+	return Command{
+		0: flags<<16 | tag,
+		1: math.Float32bits(start.X),
+		2: math.Float32bits(start.Y),
+		3: math.Float32bits(end.X),
+		4: math.Float32bits(end.Y),
+	}
+}
+
+func Quad(start, ctrl, end f32.Point, stroke bool) Command {
+	tag := uint32(elemFillQuad)
+	if stroke {
+		tag = elemStrokeQuad
+	}
+	return Command{
+		0: tag,
+		1: math.Float32bits(start.X),
+		2: math.Float32bits(start.Y),
+		3: math.Float32bits(ctrl.X),
+		4: math.Float32bits(ctrl.Y),
+		5: math.Float32bits(end.X),
+		6: math.Float32bits(end.Y),
+	}
+}
+
+func Transform(m f32.Affine2D) Command {
+	sx, hx, ox, hy, sy, oy := m.Elems()
+	return Command{
+		0: elemTransform,
+		1: math.Float32bits(sx),
+		2: math.Float32bits(hy),
+		3: math.Float32bits(hx),
+		4: math.Float32bits(sy),
+		5: math.Float32bits(ox),
+		6: math.Float32bits(oy),
+	}
+}
+
+func LineWidth(width float32) Command {
+	return Command{
+		0: elemLineWidth,
+		1: math.Float32bits(width),
+	}
+}
+
+func Stroke(col color.RGBA) Command {
+	return Command{
+		0: elemStroke,
+		1: uint32(col.R)<<24 | uint32(col.G)<<16 | uint32(col.B)<<8 | uint32(col.A),
+	}
+}
+
+func BeginClip(bbox f32.Rectangle) Command {
+	return Command{
+		0: elemBeginClip,
+		1: math.Float32bits(bbox.Min.X),
+		2: math.Float32bits(bbox.Min.Y),
+		3: math.Float32bits(bbox.Max.X),
+		4: math.Float32bits(bbox.Max.Y),
+	}
+}
+
+func EndClip(bbox f32.Rectangle) Command {
+	return Command{
+		0: elemEndClip,
+		1: math.Float32bits(bbox.Min.X),
+		2: math.Float32bits(bbox.Min.Y),
+		3: math.Float32bits(bbox.Max.X),
+		4: math.Float32bits(bbox.Max.Y),
+	}
+}
+
+func Fill(col color.RGBA) Command {
+	return Command{
+		0: elemFill,
+		1: uint32(col.R)<<24 | uint32(col.G)<<16 | uint32(col.B)<<8 | uint32(col.A),
+	}
+}
+
+func FillImage(index int) Command {
+	return Command{
+		0: elemFillImage,
+		1: uint32(index),
+	}
+}