gpu: optimize encodeQuadTo

name             old time/op  new time/op  delta
EncodeQuadTo-32  35.4ns ± 1%  11.9ns ± 3%  -66.34%  (p=0.008 n=5+5)

Signed-off-by: Egon Elbre <egonelbre@gmail.com>

gpu/clip_test.go

@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+package gpu
+
+import (
+	"testing"
+
+	"gioui.org/internal/f32"
+)
+
+func BenchmarkEncodeQuadTo(b *testing.B) {
+	var data [vertStride * 4]byte
+	for i := 0; i < b.N; i++ {
+		v := float32(i)
+		encodeQuadTo(data[:], 123,
+			f32.Point{X: v, Y: v},
+			f32.Point{X: v, Y: v},
+			f32.Point{X: v, Y: v},
+		)
+	}
+}