Added workarounds for two MBX/SGX specific GL ES bugs/problems.

The workaround flags are put into the platform independent section
for now, since there might be a general need for these as we expand
our GL and GL ES usage. The workaround_needsFullClearOnEveryFrame flag
covers the case where you get a performance penalty on PowerVR hw
if all rendering buffers are not cleared. The
workaround_brokenFBOReadBack flag covers the case where copying pixels
from a texture (e.g. via glCopyTexSubImage2d()) bound in an FBO doesn't
work.

Task-number: QTBUG-10670
Reviewed-by: Gunnar

7 files changed, 39 insertions, 18 deletions

diff --git a/src/opengl/gl2paintengineex/qtextureglyphcache_gl.cpp b/src/opengl/gl2paintengineex/qtextureglyphcache_gl.cpp
index 452d37d..cc42c63 100644
--- a/src/opengl/gl2paintengineex/qtextureglyphcache_gl.cpp
+++ b/src/opengl/gl2paintengineex/qtextureglyphcache_gl.cpp
@@ -57,21 +57,13 @@ QGLTextureGlyphCache::QGLTextureGlyphCache(QGLContext *context, QFontEngineGlyph
     , ctx(context)
     , m_width(0)
     , m_height(0)
-    , m_broken_fbo_readback(false)
 {
     // broken FBO readback is a bug in the SGX 1.3 and 1.4 drivers for the N900 where
     // copying between FBO's is broken if the texture is either GL_ALPHA or POT. The
     // workaround is to use a system-memory copy of the glyph cache for this device.
     // Switching to NPOT and GL_RGBA would both cost a lot more graphics memory and
     // be slower, so that is not desireable.
-#if defined QT_OPENGL_ES_2 && !defined(QT_NO_EGL)
-    if (QByteArray((char*) glGetString(GL_RENDERER)).contains("SGX")) {
-        QGLContextPrivate *ctxd = context->d_func();
-        m_broken_fbo_readback = QByteArray((char *) eglQueryString(ctxd->eglContext->display(), EGL_VERSION)).contains("1.3");
-    }
-#endif
-
-    if (!m_broken_fbo_readback)
+    if (!ctx->d_ptr->workaround_brokenFBOReadBack)
         glGenFramebuffers(1, &m_fbo);
 
     connect(QGLSignalProxy::instance(), SIGNAL(aboutToDestroyContext(const QGLContext*)),
@@ -83,7 +75,7 @@ QGLTextureGlyphCache::~QGLTextureGlyphCache()
     if (ctx) {
         QGLShareContextScope scope(ctx);
 
-        if (!m_broken_fbo_readback)
+        if (!ctx->d_ptr->workaround_brokenFBOReadBack)
             glDeleteFramebuffers(1, &m_fbo);
 
         if (m_width || m_height)
@@ -96,7 +88,7 @@ void QGLTextureGlyphCache::createTextureData(int width, int height)
     // create in QImageTextureGlyphCache baseclass is meant to be called
     // only to create the initial image and does not preserve the content,
     // so we don't call when this function is called from resize.
-    if (m_broken_fbo_readback && image().isNull())
+    if (ctx->d_ptr->workaround_brokenFBOReadBack && image().isNull())
         QImageTextureGlyphCache::createTextureData(width, height);
 
     glGenTextures(1, &m_texture);
@@ -126,7 +118,7 @@ void QGLTextureGlyphCache::resizeTextureData(int width, int height)
     GLuint oldTexture = m_texture;
     createTextureData(width, height);
     
-    if (m_broken_fbo_readback) {
+    if (ctx->d_ptr->workaround_brokenFBOReadBack) {
         QImageTextureGlyphCache::resizeTextureData(width, height);
         Q_ASSERT(image().depth() == 8);
         glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, oldWidth, oldHeight, GL_ALPHA, GL_UNSIGNED_BYTE, image().constBits());
@@ -209,7 +201,7 @@ void QGLTextureGlyphCache::resizeTextureData(int width, int height)
 
 void QGLTextureGlyphCache::fillTexture(const Coord &c, glyph_t glyph)
 {
-    if (m_broken_fbo_readback) {
+    if (ctx->d_ptr->workaround_brokenFBOReadBack) {
         QImageTextureGlyphCache::fillTexture(c, glyph);
 
         glBindTexture(GL_TEXTURE_2D, m_texture);
diff --git a/src/opengl/gl2paintengineex/qtextureglyphcache_gl_p.h b/src/opengl/gl2paintengineex/qtextureglyphcache_gl_p.h
index efb7435..6bcd655 100644
--- a/src/opengl/gl2paintengineex/qtextureglyphcache_gl_p.h
+++ b/src/opengl/gl2paintengineex/qtextureglyphcache_gl_p.h
@@ -115,8 +115,6 @@ private:
     int m_height;
 
     QGLShaderProgram *m_program;
-
-    bool m_broken_fbo_readback;
 };
 
 QT_END_NAMESPACE
diff --git a/src/opengl/qgl.cpp b/src/opengl/qgl.cpp
index 7c457de..922a96c 100644
--- a/src/opengl/qgl.cpp
+++ b/src/opengl/qgl.cpp
@@ -1612,6 +1612,9 @@ void QGLContextPrivate::init(QPaintDevice *dev, const QGLFormat &format)
     current_fbo = 0;
     default_fbo = 0;
     active_engine = 0;
+    workaround_needsFullClearOnEveryFrame = false;
+    workaround_brokenFBOReadBack = false;
+    workaroundsCached = false;
     for (int i = 0; i < QT_GL_VERTEX_ARRAY_TRACKED_COUNT; ++i)
         vertexAttributeArraysEnabledState[i] = false;
 }
diff --git a/src/opengl/qgl.h b/src/opengl/qgl.h
index 92a064f..f297009 100644
--- a/src/opengl/qgl.h
+++ b/src/opengl/qgl.h
@@ -431,6 +431,7 @@ private:
     friend class QGLFramebufferObjectPrivate;
     friend class QGLFBOGLPaintDevice;
     friend class QGLPaintDevice;
+    friend class QGLWidgetGLPaintDevice;
     friend class QX11GLPixmapData;
     friend class QX11GLSharedContexts;
 private:
diff --git a/src/opengl/qgl_egl.cpp b/src/opengl/qgl_egl.cpp
index 0fbbbf9..44e8ae9 100644
--- a/src/opengl/qgl_egl.cpp
+++ b/src/opengl/qgl_egl.cpp
@@ -185,8 +185,26 @@ void QGLContext::makeCurrent()
         return;
     }
 
-    if (d->eglContext->makeCurrent(d->eglSurfaceForDevice()))
+    if (d->eglContext->makeCurrent(d->eglSurfaceForDevice())) {
         QGLContextPrivate::setCurrentContext(this);
+        if (!d->workaroundsCached) {
+            d->workaroundsCached = true;
+            const char *renderer = reinterpret_cast<const char *>(glGetString(GL_RENDERER));
+            if (strstr(renderer, "SGX") || strstr(renderer, "MBX")) {
+                // PowerVR MBX/SGX chips needs to clear all buffers when starting to render
+                // a new frame, otherwise there will be a performance penalty to pay for
+                // each frame.
+                d->workaround_needsFullClearOnEveryFrame = true;
+
+                // Older PowerVR SGX drivers (like the one in the N900) have a
+                // bug which prevents glCopyTexSubImage2D() to work with a POT
+                // or GL_ALPHA texture bound to an FBO. The only way to
+                // identify that driver is to check the EGL version number for it.
+                if (strstr(eglQueryString(d->eglContext->display(), EGL_VERSION), "1.3"))
+                    d->workaround_brokenFBOReadBack = true;
+            }
+        }
+    }
 }
 
 void QGLContext::doneCurrent()
diff --git a/src/opengl/qgl_p.h b/src/opengl/qgl_p.h
index f19e394..d92f963 100644
--- a/src/opengl/qgl_p.h
+++ b/src/opengl/qgl_p.h
@@ -345,7 +345,7 @@ public:
     HDC hbitmap_hdc;
 #endif
 #ifndef QT_NO_EGL
-    bool ownsEglContext;
+    uint ownsEglContext : 1;
     QEglContext *eglContext;
     EGLSurface eglSurface;
     void destroyEglSurfaceForDevice();
@@ -382,6 +382,12 @@ public:
     uint internal_context : 1;
     uint version_flags_cached : 1;
     uint extension_flags_cached : 1;
+
+    // workarounds for driver/hw bugs on different platforms
+    uint workaround_needsFullClearOnEveryFrame : 1;
+    uint workaround_brokenFBOReadBack : 1;
+    uint workaroundsCached : 1;
+
     QPaintDevice *paintDevice;
     QColor transpColor;
     QGLContext *q_ptr;
diff --git a/src/opengl/qglpaintdevice.cpp b/src/opengl/qglpaintdevice.cpp
index e874e85..e1dcbfd 100644
--- a/src/opengl/qglpaintdevice.cpp
+++ b/src/opengl/qglpaintdevice.cpp
@@ -175,7 +175,10 @@ void QGLWidgetGLPaintDevice::beginPaint()
             float alpha = c.alphaF();
             glClearColor(c.redF() * alpha, c.greenF() * alpha, c.blueF() * alpha, alpha);
         }
-        glClear(GL_COLOR_BUFFER_BIT);
+        if (context()->d_func()->workaround_needsFullClearOnEveryFrame)
+            glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
+        else
+            glClear(GL_COLOR_BUFFER_BIT);
     }
 }