Fix conflicting DEPTH/STENCIL/DEPTH_STENCIL attachments warning

The hack, to convert two consecutive calls to glFramebufferRenderbuffer
with parameters GL_STENCIL_ATTACHMENT and GL_DEPTH_ATTACHMENT, was not
working properly. Now the call using GL_DEPTH_ATTACHMENT is ignored and
the call using GL_STENCIL_ATTACHMENT is converted into a
GL_DEPTH_STENCIL_ATTACHMENT.

This fixes the QuickItem ShaderEffect using a ShaderEffectSource as
source item.

Change-Id: Ic77bedf1837e8fa3a11818e6e5aaf8d990d6b8ea
Reviewed-by: Edward Welbourne <[email protected]>

Author: jsfdez

src/plugins/platforms/webgl/webqt.jsx

@@ -498,8 +498,14 @@ window.onload = function () {
             // the depth and stencil attachment points. WebGL does not allow this. Instead,
             // we need to attach to the DEPTH_STENCIL attachment point.
             if (d.renderbufferFormat[d.boundRenderbuffer] === gl.DEPTH_STENCIL) {
-                if (attachment === gl.STENCIL_ATTACHMENT)
+                if (attachment === gl.STENCIL_ATTACHMENT) {
                     attachment = gl.DEPTH_STENCIL_ATTACHMENT;
+                } else {
+                    // Ignore this call. Qt Quick will send a new call with STENCIL_ATTACHMENT
+                    // parameter, it will be replaced by DEPTH_STENCIL_ATTACHMENT to work-around the
+                    // browser limitation.
+                    return;
+                }
             }
             gl._framebufferRenderbuffer(target, attachment, renderbuffertarget,
                                         d.renderbufferMap[renderbuffer]);