Qt Reference Documentation

geometryengine.cpp Example File

opengl/cube/geometryengine.cpp
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 #include "geometryengine.h"

 #include <QVector2D>
 #include <QVector3D>

 struct VertexData
 {
     QVector3D position;
     QVector2D texCoord;
 };

 GeometryEngine::GeometryEngine() : vboIds(new GLuint[2])
 {
 }

 GeometryEngine::~GeometryEngine()
 {
     glDeleteBuffers(2, vboIds);
     delete[] vboIds;
 }

 void GeometryEngine::init()
 {
     initializeGLFunctions();

     // Generate 2 VBOs
     glGenBuffers(2, vboIds);


     // Initializes cube geometry and transfers it to VBOs
     initCubeGeometry();
 }

 void GeometryEngine::initCubeGeometry()
 {
     // For cube we would need only 8 vertices but we have to
     // duplicate vertex for each face because texture coordinate
     // is different.
     VertexData vertices[] = {
         // Vertex data for face 0
         {QVector3D(-1.0, -1.0,  1.0), QVector2D(0.0, 0.0)},  // v0
         {QVector3D( 1.0, -1.0,  1.0), QVector2D(0.33, 0.0)}, // v1
         {QVector3D(-1.0,  1.0,  1.0), QVector2D(0.0, 0.5)},  // v2
         {QVector3D( 1.0,  1.0,  1.0), QVector2D(0.33, 0.5)}, // v3

         // Vertex data for face 1
         {QVector3D( 1.0, -1.0,  1.0), QVector2D( 0.0, 0.5)}, // v4
         {QVector3D( 1.0, -1.0, -1.0), QVector2D(0.33, 0.5)}, // v5
         {QVector3D( 1.0,  1.0,  1.0), QVector2D(0.0, 1.0)},  // v6
         {QVector3D( 1.0,  1.0, -1.0), QVector2D(0.33, 1.0)}, // v7

         // Vertex data for face 2
         {QVector3D( 1.0, -1.0, -1.0), QVector2D(0.66, 0.5)}, // v8
         {QVector3D(-1.0, -1.0, -1.0), QVector2D(1.0, 0.5)},  // v9
         {QVector3D( 1.0,  1.0, -1.0), QVector2D(0.66, 1.0)}, // v10
         {QVector3D(-1.0,  1.0, -1.0), QVector2D(1.0, 1.0)},  // v11

         // Vertex data for face 3
         {QVector3D(-1.0, -1.0, -1.0), QVector2D(0.66, 0.0)}, // v12
         {QVector3D(-1.0, -1.0,  1.0), QVector2D(1.0, 0.0)},  // v13
         {QVector3D(-1.0,  1.0, -1.0), QVector2D(0.66, 0.5)}, // v14
         {QVector3D(-1.0,  1.0,  1.0), QVector2D(1.0, 0.5)},  // v15

         // Vertex data for face 4
         {QVector3D(-1.0, -1.0, -1.0), QVector2D(0.33, 0.0)}, // v16
         {QVector3D( 1.0, -1.0, -1.0), QVector2D(0.66, 0.0)}, // v17
         {QVector3D(-1.0, -1.0,  1.0), QVector2D(0.33, 0.5)}, // v18
         {QVector3D( 1.0, -1.0,  1.0), QVector2D(0.66, 0.5)}, // v19

         // Vertex data for face 5
         {QVector3D(-1.0,  1.0,  1.0), QVector2D(0.33, 0.5)}, // v20
         {QVector3D( 1.0,  1.0,  1.0), QVector2D(0.66, 0.5)}, // v21
         {QVector3D(-1.0,  1.0, -1.0), QVector2D(0.33, 1.0)}, // v22
         {QVector3D( 1.0,  1.0, -1.0), QVector2D(0.66, 1.0)}  // v23
     };

     // Indices for drawing cube faces using triangle strips.
     // Triangle strips can be connected by duplicating indices
     // between the strips. If connecting strips have opposite
     // vertex order then last index of the first strip and first
     // index of the second strip needs to be duplicated. If
     // connecting strips have same vertex order then only last
     // index of the first strip needs to be duplicated.
     GLushort indices[] = {
          0,  1,  2,  3,  3,     // Face 0 - triangle strip ( v0,  v1,  v2,  v3)
          4,  4,  5,  6,  7,  7, // Face 1 - triangle strip ( v4,  v5,  v6,  v7)
          8,  8,  9, 10, 11, 11, // Face 2 - triangle strip ( v8,  v9, v10, v11)
         12, 12, 13, 14, 15, 15, // Face 3 - triangle strip (v12, v13, v14, v15)
         16, 16, 17, 18, 19, 19, // Face 4 - triangle strip (v16, v17, v18, v19)
         20, 20, 21, 22, 23      // Face 5 - triangle strip (v20, v21, v22, v23)
     };

     // Transfer vertex data to VBO 0
     glBindBuffer(GL_ARRAY_BUFFER, vboIds[0]);
     glBufferData(GL_ARRAY_BUFFER, 24 * sizeof(VertexData), vertices, GL_STATIC_DRAW);

     // Transfer index data to VBO 1
     glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, vboIds[1]);
     glBufferData(GL_ELEMENT_ARRAY_BUFFER, 34 * sizeof(GLushort), indices, GL_STATIC_DRAW);
 }

 void GeometryEngine::drawCubeGeometry(QGLShaderProgram *program)
 {
     // Tell OpenGL which VBOs to use
     glBindBuffer(GL_ARRAY_BUFFER, vboIds[0]);
     glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, vboIds[1]);

     // Offset for position
     int offset = 0;

     // Tell OpenGL programmable pipeline how to locate vertex position data
     int vertexLocation = program->attributeLocation("a_position");
     program->enableAttributeArray(vertexLocation);
     glVertexAttribPointer(vertexLocation, 3, GL_FLOAT, GL_FALSE, sizeof(VertexData), (const void *)offset);

     // Offset for texture coordinate
     offset += sizeof(QVector3D);

     // Tell OpenGL programmable pipeline how to locate vertex texture coordinate data
     int texcoordLocation = program->attributeLocation("a_texcoord");
     program->enableAttributeArray(texcoordLocation);
     glVertexAttribPointer(texcoordLocation, 2, GL_FLOAT, GL_FALSE, sizeof(VertexData), (const void *)offset);

     // Draw cube geometry using indices from VBO 1
     glDrawElements(GL_TRIANGLE_STRIP, 34, GL_UNSIGNED_SHORT, 0);
 }