Qt 5.11 | Qt OpenGL | Cube OpenGL ES 2.0 example | geometryengine.cpp Example File

Qt 5.11.3 Reference Documentation

# geometryengine.cpp Example File

cube/geometryengine.cpp

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      #include "geometryengine.h"

      #include <QVector2D>
      #include <QVector3D>

      struct VertexData
      {
          QVector3D position;
          QVector2D texCoord;
      };

      GeometryEngine::GeometryEngine()
          : indexBuf(QOpenGLBuffer::IndexBuffer)
      {
          initializeOpenGLFunctions();

          // Generate 2 VBOs
          arrayBuf.create();
          indexBuf.create();

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

      GeometryEngine::~GeometryEngine()
      {
          arrayBuf.destroy();
          indexBuf.destroy();
      }

      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(-1.0f, -1.0f,  1.0f), QVector2D(0.0f, 0.0f)},  // v0
              {QVector3D( 1.0f, -1.0f,  1.0f), QVector2D(0.33f, 0.0f)}, // v1
              {QVector3D(-1.0f,  1.0f,  1.0f), QVector2D(0.0f, 0.5f)},  // v2
              {QVector3D( 1.0f,  1.0f,  1.0f), QVector2D(0.33f, 0.5f)}, // v3

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

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

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

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

              // Vertex data for face 5
              {QVector3D(-1.0f,  1.0f,  1.0f), QVector2D(0.33f, 0.5f)}, // v20
              {QVector3D( 1.0f,  1.0f,  1.0f), QVector2D(0.66f, 0.5f)}, // v21
              {QVector3D(-1.0f,  1.0f, -1.0f), QVector2D(0.33f, 1.0f)}, // v22
              {QVector3D( 1.0f,  1.0f, -1.0f), QVector2D(0.66f, 1.0f)}  // 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
          arrayBuf.bind();
          arrayBuf.allocate(vertices, 24 * sizeof(VertexData));

          // Transfer index data to VBO 1
          indexBuf.bind();
          indexBuf.allocate(indices, 34 * sizeof(GLushort));
      }

      void GeometryEngine::drawCubeGeometry(QOpenGLShaderProgram *program)
      {
          // Tell OpenGL which VBOs to use
          arrayBuf.bind();
          indexBuf.bind();

          // Offset for position
          quintptr offset = 0;

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

          // 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);
          program->setAttributeBuffer(texcoordLocation, GL_FLOAT, offset, 2, sizeof(VertexData));

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