Force max lights per layer to 2 on Vivante GLES 3.0 (i.MX6)

We have no means to figure out what's going on in the GLES implementation.
Using 3 already triggers something weird in the driver and uniform values
will not be read correctly. So stick to 2.

Change-Id: Icefa4237178bdee2b545c9bd47f1e74c80b25c04
Reviewed-by: Andy Nichols <andy.nichols@qt.io>

1 files changed, 10 insertions, 3 deletions

diff --git a/src/runtime/q3dsengine.cpp b/src/runtime/q3dsengine.cpp
index 0c14d31..20d9b0e 100644
--- a/src/runtime/q3dsengine.cpp
+++ b/src/runtime/q3dsengine.cpp
@@ -214,9 +214,9 @@ static void initGraphicsLimits(QOpenGLContext *ctx)
     gfxLimits.norm16TexturesSupported = ctx->isOpenGLES() ? extensions.contains("GL_EXT_texture_norm16") : true;
 
     // now apply some driver-specific overrides
-    if (gfxLimits.vendor.contains(QByteArrayLiteral("Vivante Corporation"))
-        && gfxLimits.version.contains(QByteArrayLiteral("OpenGL ES 3.0")))
-    {
+    const bool vivante = gfxLimits.vendor.contains(QByteArrayLiteral("Vivante Corporation"))
+        && gfxLimits.version.contains(QByteArrayLiteral("OpenGL ES 3.0"));
+    if (vivante) {
         qDebug("  found Vivante OpenGL ES 3.0, forcing OpenGL ES 2.0 rendering path");
         gfxLimits.useGles2Path = true;
     }
@@ -231,6 +231,13 @@ static void initGraphicsLimits(QOpenGLContext *ctx)
         gfxLimits.maxLightsPerLayer = 16;
     }
 
+    if (vivante) {
+        // In addition to not being able to handle GLES3.0 stuff, having a lot of uniforms
+        // makes the i.MX6 Vivante driver do weird things. Avoid this by reducing the max
+        // number of lights (and so the number of uniforms).
+        gfxLimits.maxLightsPerLayer = 2;
+    }
+
     qDebug("  use feature-limited GLES2 rendering path: %s", gfxLimits.useGles2Path ? "true" : "false");
     qDebug("  max lights per layer: %d", gfxLimits.maxLightsPerLayer);
     qDebug("  GL_MAX_DRAW_BUFFERS: %d", gfxLimits.maxDrawBuffers);