gpu: rename resourceCache to textureCache and use concrete key

The only remaining use of the cache is mapping handles to textures.
Using a concrete type for the key avoids the allocation caused by convT.

If we need more caches again in the future we can copy the type, or make
it generic.

Instead of updating the benchmark, we removed it outright. It suffered
from several flaws:

- The amount of work for each iteration of b.N wasn't constant, because
  the same cache was reused, growing ever larger in size.

- It only tested the cost of insertions. The comment "half are the same
  and half updated" wasn't true, as calling 'put' with the same key twice
  would've resulted in a panic.

- It didn't simulate any particular workload or cache size, making the
  benchmark useless for comparing different cache implementations. The
  cost of insertions isn't particularly interesting.

Signed-off-by: Dominik Honnef <dominik@honnef.co>

gpu/caches.go

@@ -8,8 +8,13 @@ import (
 	"gioui.org/internal/f32"
 )
 
-type resourceCache struct {
-	res map[interface{}]resourceCacheValue
+type textureCacheKey struct {
+	filter byte
+	handle any
+}
+
+type textureCache struct {
+	res map[textureCacheKey]resourceCacheValue
 }
 
 type resourceCacheValue struct {
@@ -37,13 +42,13 @@ type opCacheValue struct {
 	keep bool
 }
 
-func newResourceCache() *resourceCache {
-	return &resourceCache{
-		res: make(map[interface{}]resourceCacheValue),
+func newTextureCache() *textureCache {
+	return &textureCache{
+		res: make(map[textureCacheKey]resourceCacheValue),
 	}
 }
 
-func (r *resourceCache) get(key interface{}) (resource, bool) {
+func (r *textureCache) get(key textureCacheKey) (resource, bool) {
 	v, exists := r.res[key]
 	if !exists {
 		return nil, false
@@ -55,17 +60,17 @@ func (r *resourceCache) get(key interface{}) (resource, bool) {
 	return v.resource, exists
 }
 
-func (r *resourceCache) put(key interface{}, val resource) {
+func (r *textureCache) put(key textureCacheKey, val resource) {
 	v, exists := r.res[key]
 	if exists && v.used {
-		panic(fmt.Errorf("key exists, %p", key))
+		panic(fmt.Errorf("key exists, %v", key))
 	}
 	v.used = true
 	v.resource = val
 	r.res[key] = v
 }
 
-func (r *resourceCache) frame() {
+func (r *textureCache) frame() {
 	for k, v := range r.res {
 		if v.used {
 			v.used = false
@@ -77,7 +82,7 @@ func (r *resourceCache) frame() {
 	}
 }
 
-func (r *resourceCache) release() {
+func (r *textureCache) release() {
 	for _, v := range r.res {
 		v.resource.release()
 	}