用OpenGL和Vertex数组对象捕获错误

Question

我在此OpenGL实现时很难发现我的错误。当我运行程序时，我唯一得到的就是黑屏。我应该看到一个立方体。我没有遇到任何错误。我怀疑罪魁祸首可能会与vao相关：

// draws the view
-(void)drawRect:(NSRect)dirtyRect
{
// clear the viewport
glClearColor(0.0, 0.0, 0.0, 1.0);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
shaderProgramID = [self loadShaders];
// get uniform locations
uniformLocations[0] = glGetUniformLocation(shaderProgramID, "rotationX");
uniformLocations[1] = glGetUniformLocation(shaderProgramID, "rotationY");
uniformLocations[2] = glGetUniformLocation(shaderProgramID, "rotationZ");
uniformLocations[3] = glGetUniformLocation(shaderProgramID, "translation");
uniformLocations[4] = glGetUniformLocation(shaderProgramID, "projection");
// use this program
glUseProgram(shaderProgramID);
// create VAO
glGenVertexArraysAPPLE(1, &vao);
glBindVertexArrayAPPLE(vao);
glGenBuffers(3, vbo);
// bind and copy data for vertex position data
glBindBuffer(GL_ARRAY_BUFFER, vbo[0]);
glBufferData(GL_ARRAY_BUFFER, sizeof(cubePositionData), cubePositionData, GL_STATIC_DRAW);
glVertexAttribPointer(TCV_VERTEX_POS_INDEX, TCV_NUM_POS_COMPONENTS, GL_FLOAT, GL_FALSE, 0, 0);
glEnableVertexAttribArray(TCV_VERTEX_POS_INDEX);
// bind and copy data for vertex color data
glBindBuffer(GL_ARRAY_BUFFER, vbo[1]);
glBufferData(GL_ARRAY_BUFFER, sizeof(cubeColorData), cubeColorData, GL_STATIC_DRAW);
glVertexAttribPointer(TCV_VERTEX_COLOR_INDEX, TCV_NUM_COLOR_COMPONENTS, GL_FLOAT, GL_FALSE, 0, 0);
glEnableVertexAttribArray(TCV_VERTEX_COLOR_INDEX);
// bind and copy data for vertex indices data
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, vbo[2]);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(cubeIndices), cubeIndices, GL_STATIC_DRAW);
glVertexAttribPointer(TCV_VERTEX_INDICES_INDEX, TCV_NUM_INDEX_ARRAY_COMPONENTS, GL_UNSIGNED_BYTE, GL_FALSE, 0, 0);
glEnableVertexAttribArray(TCV_VERTEX_INDICES_INDEX);
// load uniform data into shader program
glUniformMatrix4fv(uniformLocations[0], 1, GL_FALSE, rotationMatX);
glUniformMatrix4fv(uniformLocations[1], 1, GL_FALSE, rotationMatY);
glUniformMatrix4fv(uniformLocations[2], 1, GL_FALSE, rotationMatZ);
glUniformMatrix4fv(uniformLocations[3], 1, GL_FALSE, translationMat);
glUniformMatrix4fv(uniformLocations[4], 1, GL_FALSE, projectionMat);
// tell OGL to draw the cube, in this order
glDrawElements(GL_TRIANGLES, 12, GL_UNSIGNED_BYTE, cubeIndices);
// unbind VAO
glBindVertexArrayAPPLE(0);
// no longer using program
glUseProgram(0);
// flush buffer
glFlush();
[[self openGLContext] flushBuffer];
}

Answer 1

我的OpenGL实验也有类似的问题。我还使用单独的缓冲对象来用于顶点位置和顶点颜色数据。我相信只有一个gl_array_buffer可以绑定到顶点数组对象。因此，将所有数据放入一个组合的缓冲区中，然后将您的属性指针设置为带有偏移的指针。

您的VBO/VAO设置应该是：

glGenVertexArrays(1, &vertexArray);
glBindVertexArray(vertexArray);
glGenBuffers(1,&vertexBuffer);
glBindBuffer(vertexBuffer);
glBindBufferData(GL_ARRAY_BUFFER, sizeof(cubePositionAndColorData), cubePositionAndColorData, GL_STATIC_DRAW);
glVertexAttribPointer(kPositionAttribute, NUM_VERTEX_COMPONENTS, GL_FLOAT, GL_FALSE, 0, 0);
// colorStartingIndex is probably just NUM_VERTEX_COMPONENTS*sizeof(GLfloat)
glVertexAttribPointer(kColorAttribute, NUM_COLOR_COMPONENTS, GL_FLOAT, GL_FALSE, 0, (void *)colorStartingIndex);
glEnableVertexAttribArray(kPositionAttribute);
glEnableVertexAttribArray(kColorAttribute);
glGenBuffers(1,&indexBuffer);
glBindBuffer(indexBuffer);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(cubeIndices), cubeIndices, GL_STATIC_DRAW);
glBindVertexArray(0);

然后，在-drawRect:功能中，您可以使用该程序，设置制服并致电glDrawElements()：

glUseProgram(shaderProgramID);
// do the necessary uniform configuration
glUniformMatrix4fv(...)
glBindVertexArray(vertexArray);
glDrawElements(GL_TRIANGLES, 12, GL_UNSIGNED_BYTE, 0);
glBindVertexArray(0);
glUseProgram(0);

另外两个值得注意的项目：

1. 我建议将所有缓冲区初始化移出您的-drawRect:方法，因为每次重新粉刷视图时都会被调用。这意味着您正在每个-drawRect:上将所有数据重新复制到OpenGL服务器。
2. 如果您使用的是OSX的最新版本，则应考虑使用最新版本的OpenGL（OpenGL/gl3.h）。