gpu: optimize pack.tryAdd

name       old time/op  new time/op  delta
Packer-32   559µs ± 2%   295µs ± 1%  -47.18%  (p=0.008 n=5+5)

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

gpu/pack_test.go

@@ -0,0 +1,30 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+package gpu
+
+import (
+	"image"
+	"testing"
+)
+
+func BenchmarkPacker(b *testing.B) {
+	var p packer
+	p.maxDims = image.Point{X: 4096, Y: 4096}
+	for i := 0; i < b.N; i++ {
+		p.clear()
+		p.newPage()
+		for k := 0; k < 500; k++ {
+			_, ok := p.tryAdd(xy(k))
+			if !ok {
+				b.Fatal("add failed", i, k, xy(k))
+			}
+		}
+	}
+}
+
+func xy(v int) image.Point {
+	return image.Point{
+		X: ((v / 16) % 16) + 8,
+		Y: (v % 16) + 8,
+	}
+}