Import glDrawBuffers() from WEBGL_draw_buffers extension (#2667)

src/glimports.h

@@ -30,6 +30,7 @@
 #define GL_IMPORT_NV___(_optional, _proto, _func) GL_EXTENSION(_optional, _proto, _func, _func ## NV)
 #define GL_IMPORT_OES__(_optional, _proto, _func) GL_EXTENSION(_optional, _proto, _func, _func ## OES)
 #define GL_IMPORT_IMG__(_optional, _proto, _func) GL_EXTENSION(_optional, _proto, _func, _func ## IMG)
+#define GL_IMPORT_WEBGL(_optional, _proto, _func) GL_EXTENSION(_optional, _proto, _func, _func ## WEBGL)
 #define GL_IMPORT_____x(_optional, _proto, _func) GL_EXTENSION(_optional, _proto, _func, _func ## XXXXX)
 
 #if GL_IMPORT_TYPEDEFS
@@ -595,7 +596,11 @@ GL_IMPORT_____x(true,  PFNGLMEMORYBARRIERPROC,                     glMemoryBarri
 GL_IMPORT_____x(true,  PFNGLDISPATCHCOMPUTEPROC,                   glDispatchCompute);
 GL_IMPORT_____x(true,  PFNGLDISPATCHCOMPUTEINDIRECTPROC,           glDispatchComputeIndirect);
 
+#if BX_PLATFORM_EMSCRIPTEN
+GL_IMPORT_WEBGL(true,  PFNGLDRAWBUFFERSPROC,                       glDrawBuffers);
+#else
 GL_IMPORT_NV___(true,  PFNGLDRAWBUFFERSPROC,                       glDrawBuffers);
+#endif
 GL_IMPORT_NV___(true,  PFNGLGENQUERIESPROC,                        glGenQueries);
 GL_IMPORT_NV___(true,  PFNGLDELETEQUERIESPROC,                     glDeleteQueries);
 GL_IMPORT_NV___(true,  PFNGLBEGINQUERYPROC,                        glBeginQuery);
@@ -671,7 +676,11 @@ GL_IMPORT______(true,  PFNGLMEMORYBARRIERPROC,                     glMemoryBarri
 GL_IMPORT______(true,  PFNGLDISPATCHCOMPUTEPROC,                   glDispatchCompute);
 GL_IMPORT______(true,  PFNGLDISPATCHCOMPUTEINDIRECTPROC,           glDispatchComputeIndirect);
 
+#	if BX_PLATFORM_EMSCRIPTEN
+GL_IMPORT_WEBGL(true,  PFNGLDRAWBUFFERSPROC,                       glDrawBuffers);
+#	else
 GL_IMPORT______(true,  PFNGLDRAWBUFFERSPROC,                       glDrawBuffers);
+#	endif
 GL_IMPORT______(true,  PFNGLGENQUERIESPROC,                        glGenQueries);
 GL_IMPORT______(true,  PFNGLDELETEQUERIESPROC,                     glDeleteQueries);
 GL_IMPORT______(true,  PFNGLBEGINQUERYPROC,                        glBeginQuery);

src/renderer_gl.cpp

@@ -6799,22 +6799,19 @@ namespace bgfx { namespace gl
 
 			m_num = uint8_t(colorIdx);
 
-			if (BX_ENABLED(BGFX_CONFIG_RENDERER_OPENGL) || s_renderGL->m_gles3 )
+			if (0 == colorIdx && BX_ENABLED(BGFX_CONFIG_RENDERER_OPENGL) )
 			{
-				if (0 == colorIdx)
-				{
-					if (BX_ENABLED(BGFX_CONFIG_RENDERER_OPENGL) )
-					{
-						// When only depth is attached disable draw buffer to avoid
-						// GL_FRAMEBUFFER_INCOMPLETE_DRAW_BUFFER.
-						GL_CHECK(glDrawBuffer(GL_NONE) );
-					}
-				}
-				else
-				{
-					GL_CHECK(glDrawBuffers(colorIdx, buffers) );
-				}
+				// When only depth is attached disable draw buffer to avoid
+				// GL_FRAMEBUFFER_INCOMPLETE_DRAW_BUFFER.
+				GL_CHECK(glDrawBuffer(GL_NONE) );
+			}
+			else if (g_caps.limits.maxFBAttachments > 0)
+			{
+				GL_CHECK(glDrawBuffers(colorIdx, buffers) );
+			}
 
+			if (BX_ENABLED(BGFX_CONFIG_RENDERER_OPENGL) || s_renderGL->m_gles3)
+			{
 				// Disable read buffer to avoid GL_FRAMEBUFFER_INCOMPLETE_READ_BUFFER.
 				GL_CHECK(glReadBuffer(GL_NONE) );
 			}