Use glDrawElements and triangle strips to draw glyphs in GL engine

We keep around a engine-global index array which we only grow when we
need to. This should hopefully speed up text drawing on some devices.

3 files changed, 34 insertions, 4 deletions

diff --git a/src/opengl/gl2paintengineex/qgl2pexvertexarray_p.h b/src/opengl/gl2paintengineex/qgl2pexvertexarray_p.h
index ae73040..d1e7615 100644
--- a/src/opengl/gl2paintengineex/qgl2pexvertexarray_p.h
+++ b/src/opengl/gl2paintengineex/qgl2pexvertexarray_p.h
@@ -118,6 +118,20 @@ public:
                     << QGLPoint(left, top);        
     }
 
+    inline void addQuad(const QRectF &rect)
+    {
+        qreal top = rect.top();
+        qreal left = rect.left();
+        qreal bottom = rect.bottom();
+        qreal right = rect.right();
+
+        vertexArray << QGLPoint(left, top)
+                    << QGLPoint(right, top)
+                    << QGLPoint(left, bottom)
+                    << QGLPoint(right, bottom);
+
+    }
+
     void addPath(const QVectorPath &path, GLfloat curveInverseScale, bool outline = true);
     void clear();
 
diff --git a/src/opengl/gl2paintengineex/qpaintengineex_opengl2.cpp b/src/opengl/gl2paintengineex/qpaintengineex_opengl2.cpp
index 18d67e9..685f0c1 100644
--- a/src/opengl/gl2paintengineex/qpaintengineex_opengl2.cpp
+++ b/src/opengl/gl2paintengineex/qpaintengineex_opengl2.cpp
@@ -1372,13 +1372,28 @@ void QGL2PaintEngineExPrivate::drawCachedGlyphs(QFontEngineGlyphCache::Type glyp
             int x = staticTextItem->glyphPositions[i].x.toInt() + c.baseLineX - margin;
             int y = staticTextItem->glyphPositions[i].y.toInt() - c.baseLineY - margin;
 
-            vertexCoordinates->addRect(QRectF(x, y, c.w, c.h));
-            textureCoordinates->addRect(QRectF(c.x*dx, c.y*dy, c.w * dx, c.h * dy));
+            vertexCoordinates->addQuad(QRectF(x, y, c.w, c.h));
+            textureCoordinates->addQuad(QRectF(c.x*dx, c.y*dy, c.w * dx, c.h * dy));
         }
 
         staticTextItem->userDataNeedsUpdate = false;
     }
 
+    if (elementIndices.size() < staticTextItem->numGlyphs*6) {
+        Q_ASSERT(elementIndices.size() % 6 == 0);
+        int j = elementIndices.size() / 6 * 4;
+        while (j < staticTextItem->numGlyphs*4) {
+            elementIndices.append(j + 0);
+            elementIndices.append(j + 0);
+            elementIndices.append(j + 1);
+            elementIndices.append(j + 2);
+            elementIndices.append(j + 3);
+            elementIndices.append(j + 3);
+
+            j += 4;
+        }
+    }
+
     setVertexAttributePointer(QT_VERTEX_COORDS_ATTR, (GLfloat*)vertexCoordinates->data());
     setVertexAttributePointer(QT_TEXTURE_COORDS_ATTR, (GLfloat*)textureCoordinates->data());
 
@@ -1454,7 +1469,7 @@ void QGL2PaintEngineExPrivate::drawCachedGlyphs(QFontEngineGlyphCache::Type glyp
             updateTextureFilter(GL_TEXTURE_2D, GL_REPEAT, false);
 
             shaderManager->currentProgram()->setUniformValue(location(QGLEngineShaderManager::MaskTexture), QT_MASK_TEXTURE_UNIT);
-            glDrawArrays(GL_TRIANGLES, 0, 6 * staticTextItem->numGlyphs);
+            glDrawElements(GL_TRIANGLE_STRIP, 6 * staticTextItem->numGlyphs, GL_UNSIGNED_SHORT, elementIndices.data());
 
             shaderManager->setMaskType(QGLEngineShaderManager::SubPixelMaskPass2);
 
@@ -1485,7 +1500,7 @@ void QGL2PaintEngineExPrivate::drawCachedGlyphs(QFontEngineGlyphCache::Type glyp
 
     shaderManager->currentProgram()->setUniformValue(location(QGLEngineShaderManager::MaskTexture), QT_MASK_TEXTURE_UNIT);
 
-    glDrawArrays(GL_TRIANGLES, 0, 6 * staticTextItem->numGlyphs);
+    glDrawElements(GL_TRIANGLE_STRIP, 6 * staticTextItem->numGlyphs, GL_UNSIGNED_SHORT, elementIndices.data());
 
     if (includeMatrixInCache)
         s->matrix = old;
diff --git a/src/opengl/gl2paintengineex/qpaintengineex_opengl2_p.h b/src/opengl/gl2paintengineex/qpaintengineex_opengl2_p.h
index 70a1621..f757bc4 100644
--- a/src/opengl/gl2paintengineex/qpaintengineex_opengl2_p.h
+++ b/src/opengl/gl2paintengineex/qpaintengineex_opengl2_p.h
@@ -267,6 +267,7 @@ public:
 
     QGL2PEXVertexArray vertexCoordinateArray;
     QGL2PEXVertexArray textureCoordinateArray;
+    QVector<GLushort> elementIndices;
     QDataBuffer<GLfloat> opacityArray;
     GLfloat staticVertexCoordinateArray[8];
     GLfloat staticTextureCoordinateArray[8];