Add experimental support for using drawElements to draw cached text

According to some design documents, drawElements() is likely to be
quicker on some devices, as the driver then does not have to create
the index array. To test the impact of this, we cache use drawElements
and cache the index array in QStaticText

1 files changed, 34 insertions, 3 deletions

diff --git a/src/opengl/gl2paintengineex/qpaintengineex_opengl2.cpp b/src/opengl/gl2paintengineex/qpaintengineex_opengl2.cpp
index eff02b2..878faf4 100644
--- a/src/opengl/gl2paintengineex/qpaintengineex_opengl2.cpp
+++ b/src/opengl/gl2paintengineex/qpaintengineex_opengl2.cpp
@@ -1276,6 +1276,8 @@ void QGL2PaintEngineEx::drawTextItem(const QPointF &p, const QTextItem &textItem
     QPaintEngineEx::drawTextItem(p, ti);
 }
 
+#define QSTATICTEXT_USE_INDEXARRAY
+
 namespace {
 
     class QOpenGLStaticTextUserData: public QStaticTextUserData
@@ -1296,6 +1298,10 @@ namespace {
         QGLContext *ctx;
         GLuint vertexCoordVBOId;
         GLuint textureCoordVBOId;
+
+#if defined(QSTATICTEXT_USE_INDEXARRAY)
+        QVector<GLubyte> indices;
+#endif
     };
 }
 
@@ -1332,12 +1338,21 @@ void QGL2PaintEngineExPrivate::drawCachedGlyphs(QFontEngineGlyphCache::Type glyp
     GLfloat dx = 1.0 / cache->width();
     GLfloat dy = 1.0 / cache->height();
 
+#if defined(QSTATICTEXT_USE_INDEXARRAY)
+    QVector<GLubyte> indices;
+#endif
+
     if (staticTextItem->userData == 0
         || staticTextItem->userData->type != QStaticTextUserData::OpenGLUserData
         || staticTextItem->userDataNeedsUpdate) {
         vertexCoordinateArray.clear();
         textureCoordinateArray.clear();
 
+#if defined(QSTATICTEXT_USE_INDEXARRAY)
+        indices.clear();
+        int j=0;
+#endif
+
         for (int i=0; i<staticTextItem->numGlyphs; ++i) {
             const QTextureGlyphCache::Coord &c = cache->coords.value(staticTextItem->glyphs[i]);
             int x = staticTextItem->glyphPositions[i].x.toInt() + c.baseLineX - margin;
@@ -1345,8 +1360,12 @@ void QGL2PaintEngineExPrivate::drawCachedGlyphs(QFontEngineGlyphCache::Type glyp
 
             vertexCoordinateArray.addRect(QRectF(x, y, c.w, c.h));
             textureCoordinateArray.addRect(QRectF(c.x*dx, c.y*dy, c.w * dx, c.h * dy));
-        }
 
+#if defined(QSTATICTEXT_USE_INDEXARRAY)
+            for (int k=0; k<6; ++k)
+                indices.append(j++);
+#endif
+        }
 
         if (staticTextItem->useBackendOptimizations) {
             QOpenGLStaticTextUserData *userData =
@@ -1370,16 +1389,19 @@ void QGL2PaintEngineExPrivate::drawCachedGlyphs(QFontEngineGlyphCache::Type glyp
             glBufferData(GL_ARRAY_BUFFER, textureCoordinateArraySize,
                          textureCoordinateArray.data(), GL_STATIC_DRAW);
 
+#if defined(QSTATICTEXT_USE_INDEXARRAY)
+            userData->indices = indices;
+#endif
+
             // If a new user data has been created, make sure we delete the old
             staticTextItem->setUserData(userData);
-            staticTextItem->userDataNeedsUpdate = false;
+            staticTextItem->userDataNeedsUpdate = false;            
 
         } else {
             setVertexAttributePointer(QT_VERTEX_COORDS_ATTR, (GLfloat*)vertexCoordinateArray.data());
             setVertexAttributePointer(QT_TEXTURE_COORDS_ATTR, (GLfloat*)textureCoordinateArray.data());
         }
     }
-
     if (staticTextItem->useBackendOptimizations) {
         Q_ASSERT(staticTextItem->userData != 0);
         Q_ASSERT(staticTextItem->userData->type == QStaticTextUserData::OpenGLUserData);
@@ -1391,6 +1413,10 @@ void QGL2PaintEngineExPrivate::drawCachedGlyphs(QFontEngineGlyphCache::Type glyp
 
         glBindBuffer(GL_ARRAY_BUFFER, userData->textureCoordVBOId);
         glVertexAttribPointer(QT_TEXTURE_COORDS_ATTR, 2, GL_FLOAT, GL_FALSE, 0, 0);
+
+#if defined(QSTATICTEXT_USE_INDEXARRAY)
+        indices = userData->indices;
+#endif
     }
 
     if (addOffset) {
@@ -1491,7 +1517,12 @@ void QGL2PaintEngineExPrivate::drawCachedGlyphs(QFontEngineGlyphCache::Type glyp
     updateTextureFilter(GL_TEXTURE_2D, GL_REPEAT, false);
 
     shaderManager->currentProgram()->setUniformValue(location(QGLEngineShaderManager::MaskTexture), QT_MASK_TEXTURE_UNIT);
+
+#if defined(QSTATICTEXT_USE_INDEXARRAY)
+    glDrawElements(GL_TRIANGLES, 6 * staticTextItem->numGlyphs, GL_UNSIGNED_BYTE, indices.constData());
+#else
     glDrawArrays(GL_TRIANGLES, 0, 6 * staticTextItem->numGlyphs);
+#endif
 
     // Reset bindings
     glBindBuffer(GL_ARRAY_BUFFER, 0);