Add support for texture pixelFormat ALPHA

h3d/impl/GlDriver.hx

@@ -374,13 +374,14 @@ class GlDriver extends Driver {
 	function getChannels( t : Texture ) {
 		return switch( t.internalFmt ) {
 		case GL.RGBA: GL.RGBA;
+		case GL.ALPHA: GL.ALPHA;
 		default: throw "Invalid format " + t.internalFmt;
 		}
 	}
 
 	override function isSupportedFormat( fmt : h3d.mat.Data.TextureFormat ) {
 		return switch( fmt ) {
-		case RGBA: true;
+		case RGBA, ALPHA: true;
 		case RGBA32F: hasFeature(FloatTextures);
 		default: false;
 		}
@@ -394,6 +395,8 @@ class GlDriver extends Driver {
 		switch( t.format ) {
 		case RGBA:
 			// default
+		case ALPHA:
+			tt.internalFmt = GL.ALPHA;
 		case RGBA32F if( hasFeature(FloatTextures) ):
 			tt.pixelFmt = GL.FLOAT;
 		default:

hxd/PixelFormat.hx

@@ -6,4 +6,5 @@ enum PixelFormat {
 	RGBA;
 	RGBA16F;
 	RGBA32F;
+	ALPHA;
 }

hxd/Pixels.hx

@@ -336,6 +336,7 @@ class Pixels {
 
 	public static function bytesPerPixel( format : PixelFormat ) {
 		return switch( format ) {
+		case ALPHA: 1;
 		case ARGB, BGRA, RGBA: 4;
 		case RGBA16F: 8;
 		case RGBA32F: 16;