SDL: Support textures regenerating when flushed

* We store a Go image.Image copy of all textures in the SDL2 renderer.
* When the underlying SDL2 textures are freed, regenerate them when
  needed from the underlying Go Image.

sdl/texture.go

@@ -14,15 +14,21 @@ import (
 func (r *Renderer) Copy(t render.Texturer, src, dst render.Rect) {
 	if tex, ok := t.(*Texture); ok {
 		var (
-			a = RectToSDL(src)
-			b = RectToSDL(dst)
+			a            = RectToSDL(src)
+			b            = RectToSDL(dst)
+			texture, err = tex.getTexture()
 		)
-		r.renderer.Copy(tex.tex, &a, &b)
+		if err == nil {
+			r.renderer.Copy(texture, &a, &b)
+		} else {
+			fmt.Printf("Renderer.Copy: texture %s could not be created: %s\n", tex.name, err)
+		}
 	}
 }
 
 // Texture can hold on to SDL textures for caching and optimization.
 type Texture struct {
+	name   string
 	render *Renderer // backref to free them up thoroughly
 	tex    *sdl.Texture
 	image  image.Image
@@ -30,13 +36,16 @@ type Texture struct {
 	height int32
 }
 
-// StoreTexture caches an SDL texture from a bitmap.
-func (r *Renderer) StoreTexture(name string, img image.Image) (render.Texturer, error) {
-	var (
-		fh = bytes.NewBuffer([]byte{})
-	)
+// Render the SDL2 Texture from the base Image if the texture is not ready.
+func (t *Texture) getTexture() (*sdl.Texture, error) {
+	if t.tex != nil {
+		return t.tex, nil
+	}
 
-	err := bmp.Encode(fh, img)
+	var (
+		fh  = bytes.NewBuffer([]byte{})
+		err = bmp.Encode(fh, t.image)
+	)
 	if err != nil {
 		return nil, fmt.Errorf("NewTexture: bmp.Encode: %s", err)
 	}
@@ -57,19 +66,30 @@ func (r *Renderer) StoreTexture(name string, img image.Image) (render.Texturer,
 	key := sdl.MapRGB(surface.Format, 255, 255, 255)
 	surface.SetColorKey(true, key)
 
-	texture, err := r.renderer.CreateTextureFromSurface(surface)
+	texture, err := t.render.renderer.CreateTextureFromSurface(surface)
 	if err != nil {
 		return nil, fmt.Errorf("NewBitmap: create texture: %s", err)
 	}
 
+	t.tex = texture
+	t.width = surface.W
+	t.height = surface.H
+	return t.tex, nil
+}
+
+// StoreTexture caches an SDL texture from a bitmap.
+func (r *Renderer) StoreTexture(name string, img image.Image) (render.Texturer, error) {
 	tex := &Texture{
+		name:   name,
 		render: r,
-		width:  surface.W,
-		height: surface.H,
-		tex:    texture,
 		image:  img,
 	}
 
+	_, err := tex.getTexture()
+	if err != nil {
+		return tex, err
+	}
+
 	r.textureMu.Lock()
 	r.textures[name] = tex
 	r.textureMu.Unlock()
@@ -120,14 +140,6 @@ func (t *Texture) Free() error {
 		t.tex = nil
 	}
 
-	// Free up the cached texture too to garbage collect the image.Image cache etc.
-	for name, tex := range t.render.textures {
-		if tex == t {
-			delete(t.render.textures, name)
-			break
-		}
-	}
-
 	return err
 }
 
@@ -139,7 +151,10 @@ func (r *Renderer) LoadTexture(name string) (render.Texturer, error) {
 	if tex, ok := r.textures[name]; ok {
 		// If the SDL2 texture had been freed, recreate it.
 		if tex.tex == nil {
-			return r.StoreTexture(name, tex.image)
+			_, err := tex.getTexture()
+			if err != nil {
+				return tex, err
+			}
 		}
 		return tex, nil
 	}
@@ -153,8 +168,11 @@ func (r *Renderer) FreeTextures() int {
 
 	var num = len(r.textures)
 	for name, tex := range r.textures {
+		if tex.tex != nil {
+			tex.tex.Destroy()
+			tex.tex = nil
+		}
 		delete(r.textures, name)
-		tex.tex.Destroy()
 	}
 	return num
 }