GL: Use MAX_DRAW_BUFFERS instead of MAX_COLOR_ATTACHMENTS.

src/renderer_gl.cpp

@@ -1199,6 +1199,8 @@ namespace bgfx { namespace gl
 				GL_GET(GL_MAX_TEXTURE_SIZE, 64);
 				GL_GET(GL_MAX_VERTEX_TEXTURE_IMAGE_UNITS, 0);
 				GL_GET(GL_MAX_RENDERBUFFER_SIZE, 1);
+				GL_GET(GL_MAX_COLOR_ATTACHMENTS, 1);
+				GL_GET(GL_MAX_DRAW_BUFFERS, 1);
 #undef GL_GET
 
 				BX_TRACE("      Vendor: %s", m_vendor);
@@ -1577,7 +1579,9 @@ namespace bgfx { namespace gl
 			||  s_extension[Extension::EXT_draw_buffers  ].m_supported
 			||  s_extension[Extension::WEBGL_draw_buffers].m_supported)
 			{
-				g_caps.maxFBAttachments = uint8_t(bx::uint32_min(glGet(GL_MAX_COLOR_ATTACHMENTS), BGFX_CONFIG_MAX_FRAME_BUFFER_ATTACHMENTS) );
+				g_caps.maxFBAttachments = uint8_t(bx::uint32_min(glGet(GL_MAX_DRAW_BUFFERS)
+						, BGFX_CONFIG_MAX_FRAME_BUFFER_ATTACHMENTS)
+						);
 			}
 
 			m_vaoSupport = !!(BGFX_CONFIG_RENDERER_OPENGLES >= 30)

src/renderer_gl.h

@@ -385,6 +385,10 @@ typedef uint64_t GLuint64;
 #	define GL_MAX_COLOR_ATTACHMENTS 0x8CDF
 #endif // GL_MAX_COLOR_ATTACHMENTS
 
+#ifndef GL_MAX_DRAW_BUFFERS
+#	define GL_MAX_DRAW_BUFFERS 0x8824
+#endif // GL_MAX_DRAW_BUFFERS
+
 #ifndef GL_QUERY_RESULT
 #	define GL_QUERY_RESULT 0x8866
 #endif // GL_QUERY_RESULT