Add FillTriangle support

OpenRA.Game/Graphics/RgbaColorRenderer.cs

@@ -200,6 +200,20 @@ namespace OpenRA.Graphics
 			DrawPolygon(new[] { tl, tr, br, bl }, width, color);
 		}
 
+		public void FillTriangle(float3 a, float3 b, float3 c, Color color)
+		{
+			color = Util.PremultiplyAlpha(color);
+			var cr = color.R / 255.0f;
+			var cg = color.G / 255.0f;
+			var cb = color.B / 255.0f;
+			var ca = color.A / 255.0f;
+
+			vertices[0] = new Vertex(a + Offset, cr, cg, cb, ca, 0, 0);
+			vertices[1] = new Vertex(b + Offset, cr, cg, cb, ca, 0, 0);
+			vertices[2] = new Vertex(c + Offset, cr, cg, cb, ca, 0, 0);
+			parent.DrawRGBAVertices(vertices);
+		}
+
 		public void FillRect(float3 tl, float3 br, Color color)
 		{
 			var tr = new float3(br.X, tl.Y, tl.Z);