ui/app/internal/gl: move single channel format detection to context

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

ui/app/internal/gpu/context.go

@@ -18,6 +18,8 @@ type caps struct {
 	// floatTriple holds the settings for floating point
 	// textures.
 	floatTriple textureTriple
+	// Single channel alpha textures.
+	alphaTriple textureTriple
 }
 
 // textureTriple holds the type settings for
@@ -57,10 +59,20 @@ func newContext(glctx gl.Context) (*context, error) {
 		EXT_disjoint_timer_query: strings.Contains(exts, "GL_EXT_disjoint_timer_query"),
 		srgbMode:                 srgbMode,
 		floatTriple:              floatTriple,
+		alphaTriple:              alphaTripleFor(ver),
 	}
 	return ctx, nil
 }
 
+func alphaTripleFor(ver [2]int) textureTriple {
+	intf, f := gl.R8, gl.Enum(gl.RED)
+	if ver[0] < 3 {
+		// R8, RED not supported on OpenGL ES 2.0.
+		intf, f = gl.LUMINANCE, gl.Enum(gl.LUMINANCE)
+	}
+	return textureTriple{intf, f, gl.UNSIGNED_BYTE}
+}
+
 func floatTripleFor(ver [2]int, exts string) (textureTriple, error) {
 	switch {
 	case ver[0] >= 3:

ui/app/internal/gpu/path.go

@@ -376,13 +376,8 @@ func loadLUT(ctx *context, lut *image.Gray) (gl.Texture, error) {
 	if lut.Stride != lut.Bounds().Dx() {
 		panic("unsupported LUT stride")
 	}
-	ver, _ := gl.ParseGLVersion(ctx.GetString(gl.VERSION))
-	intf, f := gl.R8, gl.RED
-	if ver[0] < 3 {
-		// R8, RED not supported on OpenGL ES 2.0.
-		intf, f = gl.LUMINANCE, gl.LUMINANCE
-	}
-	ctx.TexImage2D(gl.TEXTURE_2D, 0, intf, lut.Bounds().Dx(), lut.Bounds().Dy(), gl.Enum(f), gl.UNSIGNED_BYTE, lut.Pix)
+	tt := ctx.caps.alphaTriple
+	ctx.TexImage2D(gl.TEXTURE_2D, 0, tt.internalFormat, lut.Bounds().Dx(), lut.Bounds().Dy(), tt.format, tt.typ, lut.Pix)
 	ctx.PixelStorei(gl.UNPACK_ALIGNMENT, 4)
 	return tex, nil
 }