From 7297427a70a19f6da238ee77197cce68786f9076 Mon Sep 17 00:00:00 2001
From: Thomas Friedel <tomee6@gmail.com>
Date: Thu, 1 Nov 2018 17:31:36 +0100
Subject: [PATCH] fixed a bug with offscreen rendering

---
 canvas.go  | 7 ++++++-
 shadows.go | 3 +++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/canvas.go b/canvas.go
index 6898c18..a5391be 100644
--- a/canvas.go
+++ b/canvas.go
@@ -232,6 +232,7 @@ type offscreenBuffer struct {
 	h                int
 	renderStencilBuf uint32
 	frameBuf         uint32
+	alpha            bool
 }
 
 type gaussianShader struct {
@@ -607,7 +608,11 @@ func (cv *Canvas) enableTextureRenderTarget(offscr *offscreenBuffer) {
 		gli.GenTextures(1, &offscr.tex)
 		gli.BindTexture(gl_TEXTURE_2D, offscr.tex)
 		// todo do non-power-of-two textures work everywhere?
-		gli.TexImage2D(gl_TEXTURE_2D, 0, gl_RGBA, int32(cv.w), int32(cv.h), 0, gl_RGBA, gl_UNSIGNED_BYTE, nil)
+		if offscr.alpha {
+			gli.TexImage2D(gl_TEXTURE_2D, 0, gl_RGBA, int32(cv.w), int32(cv.h), 0, gl_RGBA, gl_UNSIGNED_BYTE, nil)
+		} else {
+			gli.TexImage2D(gl_TEXTURE_2D, 0, gl_RGB, int32(cv.w), int32(cv.h), 0, gl_RGB, gl_UNSIGNED_BYTE, nil)
+		}
 		gli.TexParameteri(gl_TEXTURE_2D, gl_TEXTURE_MAG_FILTER, gl_NEAREST)
 		gli.TexParameteri(gl_TEXTURE_2D, gl_TEXTURE_MIN_FILTER, gl_NEAREST)
 
diff --git a/shadows.go b/shadows.go
index 1c3e7cd..eebba96 100644
--- a/shadows.go
+++ b/shadows.go
@@ -12,6 +12,7 @@ func (cv *Canvas) drawShadow(tris []float32) {
 	}
 
 	if cv.state.shadowBlur > 0 {
+		offscr1.alpha = true
 		cv.enableTextureRenderTarget(&offscr1)
 		gli.ClearColor(0, 0, 0, 0)
 		gli.Clear(gl_COLOR_BUFFER_BIT | gl_STENCIL_BUFFER_BIT)
@@ -71,6 +72,7 @@ func (cv *Canvas) drawTextShadow(offset image.Point, strWidth, strHeight int, x,
 	y += cv.state.shadowOffsetY
 
 	if cv.state.shadowBlur > 0 {
+		offscr1.alpha = true
 		cv.enableTextureRenderTarget(&offscr1)
 		gli.ClearColor(0, 0, 0, 0)
 		gli.Clear(gl_COLOR_BUFFER_BIT | gl_STENCIL_BUFFER_BIT)
@@ -134,6 +136,7 @@ func (cv *Canvas) drawBlurredShadow() {
 
 	gaussianKernel(cv.state.shadowBlur, kernel)
 
+	offscr2.alpha = true
 	cv.enableTextureRenderTarget(&offscr2)
 	gli.ClearColor(0, 0, 0, 0)
 	gli.Clear(gl_COLOR_BUFFER_BIT | gl_STENCIL_BUFFER_BIT)