From: Mikko Rasa <tdb@tdb.fi>
Date: Tue, 11 Sep 2012 20:29:22 +0000 (+0300)
Subject: Set all color attachments of a Framebuffer as draw buffers
X-Git-Url: http://git.tdb.fi/?p=libs%2Fgl.git;a=commitdiff_plain;h=e1df3aa732d4d2d03f6ac72a8dead099937a0468

Set all color attachments of a Framebuffer as draw buffers

Indexing gl_FragData selects from the active draw buffers, so this is
required for multiple fragment shader outputs.
---

diff --git a/source/arb_draw_buffers.cpp b/source/arb_draw_buffers.cpp
new file mode 100644
index 00000000..5f843498
--- /dev/null
+++ b/source/arb_draw_buffers.cpp
@@ -0,0 +1,26 @@
+#include "arb_draw_buffers.h"
+
+namespace Msp {
+namespace GL {
+
+PFNGLDRAWBUFFERSPROC glDrawBuffers = 0;
+
+Extension::SupportLevel init_arb_draw_buffers()
+{
+	if(is_version_at_least(2, 0))
+	{
+		glDrawBuffers = reinterpret_cast<PFNGLDRAWBUFFERSPROC>(get_proc_address("glDrawBuffers"));
+		return Extension::CORE;
+	}
+	if(is_supported("GL_ARB_draw_buffers"))
+	{
+		glDrawBuffers = reinterpret_cast<PFNGLDRAWBUFFERSPROC>(get_proc_address("glDrawBuffersARB"));
+		return Extension::EXTENSION;
+	}
+	return Extension::UNSUPPORTED;
+}
+
+Extension ARB_draw_buffers("GL_ARB_draw_buffers", init_arb_draw_buffers);
+
+} // namespace GL
+} // namespace Msp
diff --git a/source/arb_draw_buffers.h b/source/arb_draw_buffers.h
new file mode 100644
index 00000000..cd2c71bc
--- /dev/null
+++ b/source/arb_draw_buffers.h
@@ -0,0 +1,18 @@
+#ifndef MSP_GL_ARB_DRAW_BUFFERS_
+#define MSP_GL_ARB_DRAW_BUFFERS_
+
+#include "extension.h"
+#include "gl.h"
+#include <GL/glext.h>
+
+namespace Msp {
+namespace GL {
+
+extern PFNGLDRAWBUFFERSPROC glDrawBuffers;
+
+extern Extension ARB_draw_buffers;
+
+} // namespace GL
+} // namespace Msp
+
+#endif
diff --git a/source/framebuffer.cpp b/source/framebuffer.cpp
index 43b0f94b..98722195 100644
--- a/source/framebuffer.cpp
+++ b/source/framebuffer.cpp
@@ -1,3 +1,4 @@
+#include "arb_draw_buffers.h"
 #include "error.h"
 #include "ext_framebuffer_blit.h"
 #include "ext_framebuffer_object.h"
@@ -46,7 +47,8 @@ void Framebuffer::update_attachment(unsigned mask) const
 {
 	if(current()==this)
 	{
-		GLenum color_buf = GL_NONE;
+		std::vector<GLenum> color_bufs;
+		color_bufs.reserve(attachments.size());
 		for(unsigned i=0; i<attachments.size(); ++i)
 		{
 			const Attachment &attch = attachments[i];
@@ -69,10 +71,18 @@ void Framebuffer::update_attachment(unsigned mask) const
 			}
 
 			if(attch.attachment>=COLOR_ATTACHMENT0 && attch.attachment<=COLOR_ATTACHMENT3)
-				color_buf = attch.attachment;
+				color_bufs.push_back(attch.attachment);
 		}
 
-		glDrawBuffer(color_buf);
+		if(color_bufs.empty())
+			glDrawBuffer(GL_NONE);
+		else if(color_bufs.size()==1)
+			glDrawBuffer(color_bufs.front());
+		else
+		{
+			static Require _req(ARB_draw_buffers);
+			glDrawBuffers(color_bufs.size(), &color_bufs[0]);
+		}
 	}
 	else
 		dirty |= mask;