OpenGL: Reinstate support for OpenGL geometry shaders

Unlike QGLShader, this requires the OpenGL 3.2 core implementation
of geometry shaders to keep the API simple.

Change-Id: Icb07f430c4c5b5d950bcf6f7119becec4cfaad8a
Reviewed-by: James Turner <james.turner@kdab.com>
Reviewed-by: Gunnar Sletta <gunnar.sletta@digia.com>

src/gui/opengl/qopengl.h

@@ -103,6 +103,7 @@ typedef GLfloat GLdouble;
 #if !defined(QT_OPENGL_ES_2)
 # if !defined(Q_OS_MAC) || (defined(Q_OS_MAC) && MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_7)
 #  define QT_OPENGL_3
+#  define QT_OPENGL_3_2
 # endif
 #endif
 

src/gui/opengl/qopenglshaderprogram.cpp

@@ -145,6 +145,8 @@ QT_BEGIN_NAMESPACE
 
     \value Vertex Vertex shader written in the OpenGL Shading Language (GLSL).
     \value Fragment Fragment shader written in the OpenGL Shading Language (GLSL).
+    \value Geometry Geometry shaders written in the OpenGL Shading Language (GLSL)
+           based on the OpenGL core feature (requires OpenGL >= 3.2).
 */
 
 class QOpenGLShaderPrivate : public QObjectPrivate
@@ -156,7 +158,17 @@ public:
         , shaderType(type)
         , compiled(false)
         , glfuncs(new QOpenGLFunctions(ctx))
+#ifndef QT_OPENGL_ES_2
+        , supportsGeometryShaders(false)
+#endif
     {
+#ifndef QT_OPENGL_ES_2
+        // Geometry shaders require OpenGL >= 3.2
+        if (shaderType & QOpenGLShader::Geometry) {
+            QSurfaceFormat f = ctx->format();
+            supportsGeometryShaders = (f.version() >= qMakePair<int, int>(3, 2));
+        }
+#endif
     }
     ~QOpenGLShaderPrivate();
 
@@ -167,6 +179,11 @@ public:
 
     QOpenGLFunctions *glfuncs;
 
+#ifndef QT_OPENGL_ES_2
+    // Support for geometry shaders
+    bool supportsGeometryShaders;
+#endif
+
     bool create();
     bool compile(QOpenGLShader *q);
     void deleteShader();
@@ -192,10 +209,15 @@ bool QOpenGLShaderPrivate::create()
     if (!context)
         return false;
     GLuint shader;
-    if (shaderType == QOpenGLShader::Vertex)
+    if (shaderType == QOpenGLShader::Vertex) {
         shader = glfuncs->glCreateShader(GL_VERTEX_SHADER);
-    else
+#if defined(QT_OPENGL_3_2)
+    } else if (shaderType == QOpenGLShader::Geometry && supportsGeometryShaders) {
+        shader = glfuncs->glCreateShader(GL_GEOMETRY_SHADER);
+#endif
+    } else {
         shader = glfuncs->glCreateShader(GL_FRAGMENT_SHADER);
+    }
     if (!shader) {
         qWarning() << "QOpenGLShader: could not create shader";
         return false;
@@ -234,6 +256,8 @@ bool QOpenGLShaderPrivate::compile(QOpenGLShader *q)
             type = types[0];
         else if (shaderType == QOpenGLShader::Vertex)
             type = types[1];
+        else if (shaderType == QOpenGLShader::Geometry)
+            type = types[2];
 
         // Get info and source code lengths
         GLint infoLogLength = 0;
@@ -2926,6 +2950,19 @@ void QOpenGLShaderProgram::setUniformValueArray(const char *name, const QMatrix4
     setUniformValueArray(uniformLocation(name), values, count);
 }
 
+/*!
+    Returns the hardware limit for how many vertices a geometry shader
+    can output.
+*/
+int QOpenGLShaderProgram::maxGeometryOutputVertices() const
+{
+    GLint n = 0;
+#if defined(QT_OPENGL_3_2)
+    glGetIntegerv(GL_MAX_GEOMETRY_OUTPUT_VERTICES, &n);
+#endif
+    return n;
+}
+
 /*!
     Returns true if shader programs written in the OpenGL Shading
     Language (GLSL) are supported on this system; false otherwise.
@@ -2972,9 +3009,22 @@ bool QOpenGLShader::hasOpenGLShaders(ShaderType type, QOpenGLContext *context)
     if (!context)
         return false;
 
-    if ((type & ~(Vertex | Fragment)) || type == 0)
+    if ((type & ~(Geometry | Vertex | Fragment)) || type == 0)
         return false;
 
+    if (type == Geometry) {
+#ifndef QT_OPENGL_ES_2
+        // Geometry shaders require OpenGL 3.2 or newer
+        QSurfaceFormat format = context->format();
+        return (format.version() >= qMakePair<int, int>(3, 2));
+#else
+        // No geometry shader support in OpenGL ES2
+        return false;
+#endif
+    }
+
+    // Unconditional support of vertex and fragment shaders implicitly assumes
+    // a minimum OpenGL version of 2.0
     return true;
 }
 

src/gui/opengl/qopenglshaderprogram.h

@@ -64,7 +64,8 @@ public:
     enum ShaderTypeBit
     {
         Vertex          = 0x0001,
-        Fragment        = 0x0002
+        Fragment        = 0x0002,
+        Geometry        = 0x0004
     };
     Q_DECLARE_FLAGS(ShaderType, ShaderTypeBit)
 
@@ -126,6 +127,8 @@ public:
 
     GLuint programId() const;
 
+    int maxGeometryOutputVertices() const;
+
     void bindAttributeLocation(const char *name, int location);
     void bindAttributeLocation(const QByteArray& name, int location);
     void bindAttributeLocation(const QString& name, int location);