Resurrect QGLWidget::renderText()

The variant taking x, y, z has been broken in all Qt 5.x releases.
This is now corrected by making the GL2 paint engine capable of applying
a Z translation.

Task-number: QTBUG-31156
Change-Id: I119566e9e9577f6cdf7e8bae56cac1e34995e622
Reviewed-by: Jørgen Lind <jorgen.lind@digia.com>

src/opengl/gl2paintengineex/qglengineshadermanager.cpp

@@ -534,7 +534,8 @@ GLuint QGLEngineShaderManager::getUniformLocation(Uniform id)
         "invertedTextureSize",
         "brushTransform",
         "brushTexture",
-        "matrix"
+        "matrix",
+        "translateZ"
     };
 
     if (uniformLocations.at(id) == GLuint(-1))

src/opengl/gl2paintengineex/qglengineshadermanager_p.h

@@ -444,6 +444,7 @@ public:
         BrushTransform,
         BrushTexture,
         Matrix,
+        TranslateZ,
         NumUniforms
     };
 

src/opengl/gl2paintengineex/qglengineshadersource_p.h

@@ -106,10 +106,13 @@ static const char* const qglslPositionOnlyVertexShader = "\n\
 
 static const char* const qglslComplexGeometryPositionOnlyVertexShader = "\n\
     uniform highp mat3 matrix; \n\
+    uniform highp float translateZ; \n\
     attribute highp vec2 vertexCoordsArray; \n\
     void setPosition(void) \n\
     { \n\
-      gl_Position = vec4(matrix * vec3(vertexCoordsArray, 1), 1);\n\
+      vec3 v = matrix * vec3(vertexCoordsArray, 1.0); \n\
+      vec4 vz = mat4(1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, translateZ, 1) * vec4(v, 1.0); \n\
+      gl_Position = vec4(vz.xyz, 1.0);\n\
     } \n";
 
 static const char* const qglslUntransformedPositionVertexShader = "\n\

src/opengl/gl2paintengineex/qpaintengineex_opengl2.cpp

@@ -1158,6 +1158,7 @@ bool QGL2PaintEngineExPrivate::prepareForDraw(bool srcPixelsAreOpaque)
         brushUniformsDirty = true;
         opacityUniformDirty = true;
         matrixUniformDirty = true;
+        translateZUniformDirty = true;
     }
 
     if (brushUniformsDirty && mode != ImageDrawingMode && mode != ImageArrayDrawingMode)
@@ -1174,6 +1175,12 @@ bool QGL2PaintEngineExPrivate::prepareForDraw(bool srcPixelsAreOpaque)
         matrixUniformDirty = false;
     }
 
+    if (translateZUniformDirty && shaderManager->hasComplexGeometry()) {
+        shaderManager->currentProgram()->setUniformValue(location(QGLEngineShaderManager::TranslateZ),
+                                                         translateZ);
+        translateZUniformDirty = false;
+    }
+
     return changed;
 }
 
@@ -2011,6 +2018,7 @@ bool QGL2PaintEngineEx::begin(QPaintDevice *pdev)
     d->matrixDirty = true;
     d->compositionModeDirty = true;
     d->opacityUniformDirty = true;
+    d->translateZUniformDirty = true;
     d->needsSync = true;
     d->useSystemClip = !systemClip().isEmpty();
     d->currentBrush = QBrush();
@@ -2375,6 +2383,15 @@ void QGL2PaintEngineExPrivate::systemStateChanged()
     }
 }
 
+void QGL2PaintEngineEx::setTranslateZ(GLfloat z)
+{
+    Q_D(QGL2PaintEngineEx);
+    if (d->translateZ != z) {
+        d->translateZ = z;
+        d->translateZUniformDirty = true;
+    }
+}
+
 void QGL2PaintEngineEx::setState(QPainterState *new_state)
 {
     //     qDebug("QGL2PaintEngineEx::setState()");

src/opengl/gl2paintengineex/qpaintengineex_opengl2_p.h

@@ -158,6 +158,9 @@ public:
     bool isNativePaintingActive() const;
     bool requiresPretransformedGlyphPositions(QFontEngine *, const QTransform &) const { return false; }
     bool shouldDrawCachedGlyphs(QFontEngine *, const QTransform &) const;
+
+    void setTranslateZ(GLfloat z);
+
 private:
     Q_DISABLE_COPY(QGL2PaintEngineEx)
 };
@@ -183,7 +186,8 @@ public:
             snapToPixelGrid(false),
             nativePaintingActive(false),
             inverseScale(1),
-            lastMaskTextureUsed(0)
+            lastMaskTextureUsed(0),
+            translateZ(0)
     { }
 
     ~QGL2PaintEngineExPrivate();
@@ -266,6 +270,7 @@ public:
     bool brushUniformsDirty;
     bool opacityUniformDirty;
     bool matrixUniformDirty;
+    bool translateZUniformDirty;
 
     bool stencilClean; // Has the stencil not been used for clipping so far?
     bool useSystemClip;
@@ -309,6 +314,8 @@ public:
     QVector<GLuint> unusedIBOSToClean;
 
     const GLfloat *vertexAttribPointers[3];
+
+    GLfloat translateZ;
 };
 
 

src/opengl/qgl.cpp

@@ -4451,12 +4451,6 @@ void QGLWidget::renderText(int x, int y, const QString &str, const QFont &font)
 
             glDisable(GL_DEPTH_TEST);
             glViewport(0, 0, width, height);
-            glMatrixMode(GL_PROJECTION);
-            glLoadIdentity();
-            glOrtho(0, width, height, 0, 0, 1);
-            glMatrixMode(GL_MODELVIEW);
-
-            glLoadIdentity();
         } else {
             setAutoBufferSwap(false);
             // disable glClear() as a result of QPainter::begin()
@@ -4567,19 +4561,21 @@ void QGLWidget::renderText(double x, double y, double z, const QString &str, con
         } else if (use_scissor_testing) {
             glEnable(GL_SCISSOR_TEST);
         }
-        glMatrixMode(GL_PROJECTION);
-        glLoadIdentity();
         glViewport(0, 0, width, height);
-        glOrtho(0, width, height, 0, 0, 1);
-        glMatrixMode(GL_MODELVIEW);
-        glLoadIdentity();
         glAlphaFunc(GL_GREATER, 0.0);
         glEnable(GL_ALPHA_TEST);
         if (use_depth_testing)
             glEnable(GL_DEPTH_TEST);
-        glTranslated(0, 0, -win_z);
+
+        // The only option in Qt 5 is the shader-based OpenGL 2 paint engine.
+        // Setting fixed pipeline transformations is futile. Instead, pass the
+        // extra values directly and let the engine figure the matrices out.
+        static_cast<QGL2PaintEngineEx *>(p->paintEngine())->setTranslateZ(-win_z);
+
         qt_gl_draw_text(p, qRound(win_x), qRound(win_y), str, font);
 
+        static_cast<QGL2PaintEngineEx *>(p->paintEngine())->setTranslateZ(0);
+
         if (!reuse_painter) {
             p->end();
             delete p;