graphicscommand: Move the texel adjustment logic to graphicscommand package

This is a preparation for #879. The value of the texel adjustment
depends on the graphics driver (GLSL float precisions), and this
can be accessed only after the run loop runs. The place where
graphics commands are executed seems an appropriate place.

Updates #879

internal/graphicscommand/command.go

@@ -54,6 +54,11 @@ type command interface {
 	CanMerge(dst, src *Image, color *affine.ColorM, mode graphics.CompositeMode, filter graphics.Filter, address graphics.Address) bool
 }
 
+type size struct {
+	width  float32
+	height float32
+}
+
 // commandQueue is a command queue for drawing commands.
 type commandQueue struct {
 	// commands is a queue of drawing commands.
@@ -70,6 +75,8 @@ type commandQueue struct {
 	// Rename or fix the program.
 	nvertices int
 
+	dstSizes []size
+
 	indices  []uint16
 	nindices int
 
@@ -83,12 +90,18 @@ type commandQueue struct {
 var theCommandQueue = &commandQueue{}
 
 // appendVertices appends vertices to the queue.
-func (q *commandQueue) appendVertices(vertices []float32) {
+func (q *commandQueue) appendVertices(vertices []float32, width, height float32) {
 	if len(q.vertices) < q.nvertices+len(vertices) {
 		n := q.nvertices + len(vertices) - len(q.vertices)
 		q.vertices = append(q.vertices, make([]float32, n)...)
+		q.dstSizes = append(q.dstSizes, make([]size, n/graphics.VertexFloatNum)...)
 	}
 	copy(q.vertices[q.nvertices:], vertices)
+	for i := 0; i < len(vertices)/graphics.VertexFloatNum; i++ {
+		idx := q.nvertices/graphics.VertexFloatNum + i
+		q.dstSizes[idx].width = width
+		q.dstSizes[idx].height = height
+	}
 	q.nvertices += len(vertices)
 }
 
@@ -140,9 +153,10 @@ func (q *commandQueue) EnqueueDrawTrianglesCommand(dst, src *Image, vertices []f
 		split = true
 	}
 
-	q.appendVertices(vertices)
+	n := len(vertices) / graphics.VertexFloatNum
+	q.appendVertices(vertices, float32(dst.width), float32(dst.height))
 	q.appendIndices(indices, uint16(q.nextIndex))
-	q.nextIndex += len(vertices) / graphics.VertexFloatNum
+	q.nextIndex += n
 	q.tmpNumIndices += len(indices)
 
 	// TODO: If dst is the screen, reorder the command to be the last.
@@ -169,6 +183,15 @@ func (q *commandQueue) Flush() {
 		fmt.Println("--")
 	}
 
+	// Adjust texels.
+	// TODO: texelAdjustmentFactor can vary depends on the highp precisions (#879).
+	const texelAdjustmentFactor = 1.0 / 512.0
+	for i := 0; i < q.nvertices/graphics.VertexFloatNum; i++ {
+		s := q.dstSizes[i]
+		vs[i*graphics.VertexFloatNum+6] -= 1.0 / s.width * texelAdjustmentFactor
+		vs[i*graphics.VertexFloatNum+7] -= 1.0 / s.height * texelAdjustmentFactor
+	}
+
 	theGraphicsDriver.Begin()
 	for len(q.commands) > 0 {
 		nv := 0

internal/graphicscommand/image_test.go

@@ -49,7 +49,6 @@ type testVertexPutter struct {
 
 func (t *testVertexPutter) PutVertex(vs []float32, dx, dy, sx, sy float32, bx0, by0, bx1, by1 float32, cr, cg, cb, ca float32) {
 	// The implementation is basically same as restorable.(*Image).PutVertex.
-	// This doesn't adjust texels, but this is fine as long as the rectangle is not rotated or scaled.
 	vs[0] = dx
 	vs[1] = dy
 	vs[2] = sx / t.w

internal/restorable/image.go

@@ -240,8 +240,6 @@ func (i *Image) internalSize() (int, int) {
 }
 
 func (i *Image) PutVertex(vs []float32, dx, dy, sx, sy float32, bx0, by0, bx1, by1 float32, cr, cg, cb, ca float32) {
-	const texelAdjustmentFactor = 512.0
-
 	// Specifying a range explicitly here is redundant but this helps optimization
 	// to eliminate boundary checks.
 	//
@@ -256,8 +254,8 @@ func (i *Image) PutVertex(vs []float32, dx, dy, sx, sy float32, bx0, by0, bx1, b
 	vs[3] = sy / float32(h)
 	vs[4] = bx0 / float32(w)
 	vs[5] = by0 / float32(h)
-	vs[6] = bx1/float32(w) - 1.0/float32(w)/texelAdjustmentFactor
-	vs[7] = by1/float32(h) - 1.0/float32(h)/texelAdjustmentFactor
+	vs[6] = bx1 / float32(w)
+	vs[7] = by1 / float32(h)
 	vs[8] = cr
 	vs[9] = cg
 	vs[10] = cb