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// Copyright (C) 2022 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only
#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, nullptr);
}
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