Qtopengl，为啥不能使用不同的vbo绘制两个立方体

Posted 2023-02-14

【中文标题】Qtopengl，为啥不能使用不同的vbo绘制两个立方体

【英文标题】：Qtopengl, why can not draw two cubes using different vboQtopengl，为什么不能使用不同的vbo绘制两个立方体

【发布时间】：2019-07-18 03:07:57

【问题描述】：

我在 QT 中使用 opengl，并想绘制一个彩色立方体和一个白色立方体（模拟光源）。我使用两个不同的着色器程序和两个不同的 vbo。但是，我发现我只能画一个立方体。该怎么办？

m_shaderProgram->addShaderFromSourceFile(QOpenGLShader::Vertex, ":/shaders/vertexShader.vert");
m_shaderProgram->addShaderFromSourceFile(QOpenGLShader::Fragment, ":/shaders/fragmentShader.frag");
m_shaderProgram->link();
//m_shaderProgram->bind();
m_programId = m_shaderProgram->programId();

m_lightShaderProgram->addShaderFromSourceFile(QOpenGLShader::Vertex, ":/shaders/lightVertexShader.vert");
m_lightShaderProgram->addShaderFromSourceFile(QOpenGLShader::Fragment, ":/shaders/lightFragShader.frag");
m_lightShaderProgram->link();
//m_lightShaderProgram->bind();
m_lightProgramId = m_lightShaderProgram->programId();

GLint modelLoc = glGetUniformLocation(m_programId, "model");
GLint viewLoc = glGetUniformLocation(m_programId, "view");
GLint projectionLoc = glGetUniformLocation(m_programId, "projection");
glUniformMatrix4fv(modelLoc, 1, GL_FALSE, m_model.data());
glUniformMatrix4fv(viewLoc, 1, GL_FALSE, m_camera.getViewMatrix().data());
glUniformMatrix4fv(projectionLoc, 1, GL_FALSE, m_camera.getProjectionMatrix().data());

// light source
GLint lightModelLoc = glGetUniformLocation(m_lightProgramId, "lightModel");
GLint lightViewLoc = glGetUniformLocation(m_lightProgramId, "lightView");
GLint lightProjectionLoc = glGetUniformLocation(m_lightProgramId, "lightProjection");
glUniformMatrix4fv(lightModelLoc, 1, GL_FALSE, m_lightModel.data());
glUniformMatrix4fv(lightViewLoc, 1, GL_FALSE, m_camera.getViewMatrix().data());
glUniformMatrix4fv(lightProjectionLoc, 1, GL_FALSE, m_camera.getProjectionMatrix().data());

// draw colored cube
m_shaderProgram->bind();
glBindBuffer(GL_ARRAY_BUFFER, m_vbo);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 5 * sizeof(GLfloat), nullptr);
glEnableVertexAttribArray(0);
glDrawArrays(GL_TRIANGLES, 0, 36);
glBindBuffer(GL_ARRAY_BUFFER, 0);

// draw light source
m_lightShaderProgram->bind();
glBindBuffer(GL_ARRAY_BUFFER, m_lightVbo);
glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 5 * sizeof(GLfloat), nullptr);
glEnableVertexAttribArray(0);
glDrawArrays(GL_TRIANGLES, 0, 36);
glBindBuffer(GL_ARRAY_BUFFER, 0);

【问题讨论】：

m_vbo 和 m_lightVbo 绑定相同的顶点数据

【参考方案1】：

推荐使用QOpenGLShaderProgram对象的.setUniformValue()方法来设置制服的值。

但问题是，glUniform* 设置了当前安装程序的统一变量（在默认统一块中）的值。 在设置制服之前，您必须安装程序（glUseProgram / m_shaderProgram->bind()）：

GLint modelLoc = glGetUniformLocation(m_programId, "model");
GLint viewLoc = glGetUniformLocation(m_programId, "view");
GLint projectionLoc = glGetUniformLocation(m_programId, "projection");

GLint lightModelLoc = glGetUniformLocation(m_lightProgramId, "lightModel");
GLint lightViewLoc = glGetUniformLocation(m_lightProgramId, "lightView");
GLint lightProjectionLoc = glGetUniformLocation(m_lightProgramId, "lightProjection");

m_shaderProgram->bind();
glUniformMatrix4fv(modelLoc, 1, GL_FALSE, m_model.data());
glUniformMatrix4fv(viewLoc, 1, GL_FALSE, m_camera.getViewMatrix().data());
glUniformMatrix4fv(projectionLoc, 1, GL_FALSE, m_camera.getProjectionMatrix().data());

m_lightShaderProgram->bind();
glUniformMatrix4fv(lightModelLoc, 1, GL_FALSE, m_lightModel.data());
glUniformMatrix4fv(lightViewLoc, 1, GL_FALSE, m_camera.getViewMatrix().data());
glUniformMatrix4fv(lightProjectionLoc, 1, GL_FALSE, m_camera.getProjectionMatrix().data());