wasm: prevent WebGL vertex attribute errors

WebGL is stricter than OpenGL ES and require that unused
vertex attribute arrays are disabled. This prevents
errors such as:

  WebGL: INVALID_OPERATION: drawElements: no buffer
  is bound to enabled attribute

Pick-to: 6.3
Change-Id: I68384a9f6954b6a1960ba6e8afd1fdbdfefe2335
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>
Reviewed-by: Lorn Potter <lorn.potter@gmail.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/src/gui/rhi/qrhigles2.cpp b/src/gui/rhi/qrhigles2.cpp
index e7a2382497..adb6614336 100644
--- a/src/gui/rhi/qrhigles2.cpp
+++ b/src/gui/rhi/qrhigles2.cpp
@@ -2753,6 +2753,14 @@ void QRhiGles2::executeCommandBuffer(QRhiCommandBuffer *cb)
                     f->glVertexAttribDivisor(GLuint(i), 0);
                 state.instancedAttributesUsed = false;
             }
+#ifdef Q_OS_WASM
+            for (int i = 0; i < CommandBufferExecTrackedState::TRACKED_ATTRIB_COUNT; ++i) {
+                if (state.enabledAttribArrays[i]) {
+                    f->glDisableVertexAttribArray(GLuint(i));
+                    state.enabledAttribArrays[i] = false;
+                }
+            }
+#endif
             if (vao)
                 f->glBindVertexArray(0);
             break;