internal/rendertest: create test suit for drawing operations

Uses app/headless to create a set of test cases for drawing operations, including clipping
textures and transforms. This commit tests for approximate pixel matches, if future changes affect
local drawing operations it will be easy to change the reference images, it thus becomes and
should be an intentional operation if changes lead to local changes in drawn results.

Ideally we should be able to make the tests check for exact pixel matches down the line to ensure
consistent results between platforms.

Signed-off-by: Viktor <viktor.ogeman@gmail.com>

internal/rendertest/bench_test.go

@@ -97,6 +97,29 @@ func BenchmarkDrawUI(b *testing.B) {
 	finishBenchmark(b, w)
 }
 
+func BenchmarkDrawUITransformed(b *testing.B) {
+	// Like BenchmarkDraw UI but transformed at every frame
+	gtx, w, th := setupBenchmark(b)
+	drawCore(gtx, th)
+	w.Frame(gtx.Ops)
+	b.ReportAllocs()
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		resetOps(gtx)
+
+		p := op.Push(gtx.Ops)
+		angle := float32(math.Mod(float64(i)/1000, 0.05))
+		a := f32.Affine2D{}.Shear(f32.Point{}, angle, angle).Rotate(f32.Point{}, angle)
+		op.Affine(a).Add(gtx.Ops)
+
+		drawCore(gtx, th)
+
+		p.Pop()
+		w.Frame(gtx.Ops)
+	}
+	finishBenchmark(b, w)
+}
+
 func Benchmark1000Circles(b *testing.B) {
 	// Benchmark1000Shapes draws 1000 individual shapes such that no caching between
 	// shapes will be possible and resets buffers on each operation to prevent caching