gpu: add binding flags to Backend.NewTexture

Direct3D needs to know the texture bind usage up front, in particular
whether the texture is going to be used as a render target.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

gpu/backend.go

@@ -18,7 +18,7 @@ type Backend interface {
 	// IsContinuousTime reports whether all timer measurements
 	// are valid at the point of call.
 	IsTimeContinuous() bool
-	NewTexture(format TextureFormat, width, height int, minFilter, magFilter TextureFilter) Texture
+	NewTexture(format TextureFormat, width, height int, minFilter, magFilter TextureFilter, bindings BufferBinding) Texture
 	DefaultFramebuffer() Framebuffer
 	NewFramebuffer() Framebuffer
 	NewImmutableBuffer(typ BufferBinding, data []byte) Buffer
@@ -162,6 +162,8 @@ const (
 	BufferBindingIndices BufferBinding = 1 << iota
 	BufferBindingVertices
 	BufferBindingUniforms
+	BufferBindingTexture
+	BufferBindingFramebuffer
 )
 
 const (

gpu/gl/backend.go

@@ -171,7 +171,7 @@ func (b *Backend) DefaultFramebuffer() gpu.Framebuffer {
 	return b.defFBO
 }
 
-func (b *Backend) NewTexture(format gpu.TextureFormat, width, height int, minFilter, magFilter gpu.TextureFilter) gpu.Texture {
+func (b *Backend) NewTexture(format gpu.TextureFormat, width, height int, minFilter, magFilter gpu.TextureFilter, binding gpu.BufferBinding) gpu.Texture {
 	tex := &gpuTexture{backend: b, obj: b.funcs.CreateTexture()}
 	switch format {
 	case gpu.TextureFormatFloat:

gpu/gpu.go

@@ -378,7 +378,7 @@ func (r *renderer) texHandle(t *texture) Texture {
 	if t.tex != nil {
 		return t.tex
 	}
-	t.tex = r.ctx.NewTexture(TextureFormatSRGB, t.src.Bounds().Dx(), t.src.Bounds().Dy(), FilterLinear, FilterLinear)
+	t.tex = r.ctx.NewTexture(TextureFormatSRGB, t.src.Bounds().Dx(), t.src.Bounds().Dy(), FilterLinear, FilterLinear, BufferBindingTexture)
 	t.tex.Upload(t.src)
 	return t.tex
 }

gpu/path.go

@@ -210,7 +210,8 @@ func (s *fboSet) resize(ctx Backend, sizes []image.Point) {
 				f.tex.Release()
 			}
 			f.size = sz
-			f.tex = ctx.NewTexture(TextureFormatFloat, sz.X, sz.Y, FilterNearest, FilterNearest)
+			f.tex = ctx.NewTexture(TextureFormatFloat, sz.X, sz.Y, FilterNearest, FilterNearest,
+				BufferBindingTexture|BufferBindingFramebuffer)
 			f.fbo.BindTexture(f.tex)
 		}
 	}