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++ // Copyright (C) 2016 The Qt Company Ltd.
++ // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
++
++ #include "geometryengine.h"
++
++ #include <QVector2D>
++ #include <QVector3D>
++
++ struct VertexData
++ {
++ QVector3D position;
++ QVector2D texCoord;
++ };
++
++ //! [0]
++ 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();
++ }
++ //! [0]
++
++ 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)
++ };
++
++ //! [1]
++ // 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));
++ //! [1]
++ }
++
++ //! [2]
++ 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, nullptr);
++ }
++ //! [2]