gpu: fix clip intersection with the D3D backend

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

app/headless/headless_test.go

@@ -9,6 +9,7 @@ import (
 
 	"gioui.org/f32"
 	"gioui.org/op"
+	"gioui.org/op/clip"
 	"gioui.org/op/paint"
 )
 
@@ -39,6 +40,64 @@ func TestHeadless(t *testing.T) {
 	}
 }
 
+func TestClipping(t *testing.T) {
+	w, release := newTestWindow(t)
+	defer release()
+
+	sz := w.size
+	col := color.RGBA{A: 0xff, R: 0xca, G: 0xfe}
+	col2 := color.RGBA{A: 0xff, R: 0x00, G: 0xfe}
+	var ops op.Ops
+	pop := paint.PaintOp{Rect: f32.Rectangle{Max: f32.Point{
+		X: float32(sz.X),
+		Y: float32(sz.Y),
+	}}}
+	paint.ColorOp{Color: col}.Add(&ops)
+	clip.Rect{
+		Rect: f32.Rectangle{
+			Min: f32.Point{X: 50, Y: 50},
+			Max: f32.Point{X: 250, Y: 250},
+		},
+		SE: 75,
+	}.Op(&ops).Add(&ops)
+	pop.Add(&ops)
+	paint.ColorOp{Color: col2}.Add(&ops)
+	clip.Rect{
+		Rect: f32.Rectangle{
+			Min: f32.Point{X: 100, Y: 100},
+			Max: f32.Point{X: 350, Y: 350},
+		},
+		NW: 75,
+	}.Op(&ops).Add(&ops)
+	pop.Add(&ops)
+	w.Frame(&ops)
+
+	img, err := w.Screenshot()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if *dumpImages {
+		if err := saveImage("clip.png", img); err != nil {
+			t.Fatal(err)
+		}
+	}
+	bg := color.RGBA{A: 0xff, R: 0xff, G: 0xff, B: 0xff}
+	tests := []struct {
+		x, y  int
+		color color.RGBA
+	}{
+		{120, 120, col},
+		{130, 130, col2},
+		{210, 210, col2},
+		{230, 230, bg},
+	}
+	for _, test := range tests {
+		if got := img.RGBAAt(test.x, test.y); got != test.color {
+			t.Errorf("(%d,%d): got color %v, expected %v", test.x, test.y, got, test.color)
+		}
+	}
+}
+
 func newTestWindow(t *testing.T) (*Window, func()) {
 	t.Helper()
 	sz := image.Point{X: 800, Y: 600}

gpu/gpu.go

@@ -538,15 +538,21 @@ func (r *renderer) intersectPath(p *pathOp, clip image.Rectangle) {
 	if !p.path {
 		return
 	}
-	o := p.place.Pos.Add(clip.Min).Sub(p.clip.Min)
 	uv := image.Rectangle{
+		Min: p.place.Pos,
+		Max: p.place.Pos.Add(p.clip.Size()),
+	}
+	o := clip.Min.Sub(p.clip.Min)
+	sub := image.Rectangle{
 		Min: o,
 		Max: o.Add(clip.Size()),
 	}
 	fbo := r.pather.stenciler.cover(p.place.Idx)
 	r.ctx.BindTexture(0, fbo.tex)
 	coverScale, coverOff := texSpaceTransform(toRectF(uv), fbo.size)
+	subScale, subOff := texSpaceTransform(toRectF(sub), p.clip.Size())
 	r.pather.stenciler.iprog.uniforms.vert.uvTransform = [4]float32{coverScale.X, coverScale.Y, coverOff.X, coverOff.Y}
+	r.pather.stenciler.iprog.uniforms.vert.subUVTransform = [4]float32{subScale.X, subScale.Y, subOff.X, subOff.Y}
 	r.pather.stenciler.iprog.prog.UploadUniforms()
 	r.ctx.DrawArrays(backend.DrawModeTriangleStrip, 0, 4)
 }

gpu/path.go

@@ -83,7 +83,8 @@ type stencilUniforms struct {
 
 type intersectUniforms struct {
 	vert struct {
-		uvTransform [4]float32
+		uvTransform    [4]float32
+		subUVTransform [4]float32
 	}
 }
 

gpu/shaders/common.inc

@@ -17,6 +17,23 @@ vec3[2] fboTextureTransform() {
 	return t;
 }
 
+// fboTransform returns a transformation
+// that cancels the implied transformation between
+// the clip space and the framebuffer.
+// Only two rows are returned. The last is implied
+// to be [0, 0, 1].
+vec3[2] fboTransform() {
+	vec3[2] t;
+#ifdef HLSL
+	t[0] = vec3(1.0, 0.0, 0.0);
+	t[1] = vec3(0.0, 1.0, 0.0);
+#else
+	t[0] = vec3(1.0, 0.0, 0.0);
+	t[1] = vec3(0.0, -1.0, 0.0);
+#endif
+	return t;
+}
+
 // toClipSpace converts an OpenGL gl_Position value to a
 // native GPU position.
 vec4 toClipSpace(vec4 pos) {

gpu/shaders/intersect.vert

@@ -4,18 +4,25 @@
 
 precision highp float;
 
+#include <common.inc>
+
 layout(location = 0) in vec2 pos;
 layout(location = 1) in vec2 uv;
 
 layout(binding = 0) uniform Block {
 	vec4 uvTransform;
+	vec4 subUVTransform;
 };
 
 layout(location = 0) out vec2 vUV;
 
 void main() {
-  vec2 p = pos;
-  p.y = -p.y;
-  gl_Position = vec4(p, 0, 1);
-  vUV = uv*uvTransform.xy + uvTransform.zw;
+  vec3[2] fboTrans = fboTransform();
+  vec3 p = transform3x2(fboTrans, vec3(pos, 1.0));
+  gl_Position = vec4(p, 1);
+  vec3[2] fboTexTrans = fboTextureTransform();
+  vec3 uv3 = transform3x2(fboTexTrans, vec3(uv, 1.0));
+  vUV = uv3.xy*subUVTransform.xy + subUVTransform.zw;
+  vUV = transform3x2(fboTexTrans, vec3(vUV, 1.0)).xy;
+  vUV = vUV*uvTransform.xy + uvTransform.zw;
 }