Use GL_ARB_draw_buffers if avaliable

Author: MAJigsaw77

src/openfl/display/OpenGLRenderer.hx

@@ -52,6 +52,8 @@ class OpenGLRenderer extends DisplayObjectRenderer
 	@:noCompletion private static var __complexBlendsSupported:Null<Bool>;
 	@:noCompletion private static var __coherentBlendsSupported:Null<Bool>;
 	@:noCompletion private static var __sRGBWriteControlSupported:Null<Bool>;
+	@:noCompletion private static var __drawBuffersARB:Null<Bool>;
+	@:noCompletion private static var __drawBuffersEXT:Null<Bool>;
 
 	@:noCompletion private static var __alphaValue:Array<Float> = [1];
 	@:noCompletion private static var __colorMultipliersValue:Array<Float> = [0, 0, 0, 0];
@@ -167,6 +169,14 @@ class OpenGLRenderer extends DisplayObjectRenderer
 		{
 			__standardDerivativesSupported = exts.contains("OES_standard_derivatives");
 		}
+		if (__drawBuffersARB == null)
+		{
+			__drawBuffersARB = exts.contains("ARB_draw_buffers");
+		}
+		if (__drawBuffersEXT == null)
+		{
+			__drawBuffersEXT = exts.contains("EXT_draw_buffers");
+		}
 
 		#if (js && html5)
 		__softwareRenderer = new CanvasRenderer(null);

src/openfl/display/Shader.hx

@@ -567,7 +567,14 @@ class Shader
 			extensions += "#extension GL_OES_standard_derivatives : enable\n";
 		}
 
-		extensions += "#extension GL_EXT_draw_buffers : enable\n";
+		if (OpenGLRenderer.__drawBuffersARB)
+		{
+			extensions += "#extension GL_ARB_draw_buffers : enable\n";
+		}
+		else if (OpenGLRenderer.__drawBuffersEXT == null)
+		{
+			extensions += "#extension GL_EXT_draw_buffers : enable\n";
+		}
 
 		// #version must be the first directive and cannot be repeated,
 		// while #extension directives must be before any non-preprocessor tokens.