GLSL 1.50，openGL 3.3。
我最近一直试图让我的转换反馈工作但没有成功。在 glBeginTranformFeedback() 之后我仍然收到错误，并且由于我还没有找到任何完整的工作代码，我已经用我找到的一些代码和文档积累了我的知识，它现在应该运行良好，但我错过了一些东西。因此，如果有人有完整的代码（初始化缓冲区、设置、更新、渲染、读回），那肯定会有所帮助，如果你不知道发生了什么，你可以看看我的代码。我排除了一些基准测试、窗口处理和它的创建：
int main()
{
bool fullsize = false, paused = false;
std::string caption = "Tester";
GLuint dataVAO,speedUpdateVBO,dataVBO;
std::vector<vector3f> dataW;
// Create the main rendering window
init(); //just some camera commands
UniShader shader; //my shader class keeps everything together
shader.init();
shader.addShader("test.vert");
shader.addShader("test.frag");
shader.newAttributeVariable("speed");
shader.newFeedbackVarying("sp");
shader.linkShader();
shader.use();
//init some data
dataW.push_back(vector3f(0,1,0));
//creating VAO
glGenVertexArrays(1,&dataVAO);
glBindVertexArray(dataVAO);
//creating VBO
glGenBuffers(1,&dataVBO);
glBindBuffer(GL_ARRAY_BUFFER,dataVBO);
glBufferData(GL_ARRAY_BUFFER, sizeof(vector3f), 0, GL_DYNAMIC_DRAW);
glVertexAttribPointer(shader.getAttributeIndex("speed"), 3, GL_FLOAT, GL_FALSE, 0, 0);
glGenBuffers(1, &speedUpdateVBO);
glBindBuffer(GL_TRANSFORM_FEEDBACK_BUFFER, speedUpdateVBO);
glBufferData(GL_TRANSFORM_FEEDBACK_BUFFER, sizeof(vector3f), NULL, GL_DYNAMIC_COPY);
glBindBufferBase(GL_TRANSFORM_FEEDBACK_BUFFER, 0, speedUpdateVBO);
glBindVertexArray(0);
while (App.IsOpened())
{
App.SetActive();
benchP = Clock.GetElapsedTime();
//update calls
if(!paused)
//update
benchU = Clock.GetElapsedTime();
//render calls
glClearColor(1.0f, 1.0f, 1.0f, 0.0f);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glColor3f(0.6f,0.7f,0.7f);
GLuint query;
GLuint count = 0;
glGenQueries(1, &query);
glEnableVertexAttribArray(shader.getAttributeIndex("speed"));
glBindVertexArray(dataVAO);
glBindBuffer(GL_ARRAY_BUFFER,dataVBO);
glBufferData(GL_ARRAY_BUFFER, sizeof(vector3f)*dataW.size(), &dataW[0], GL_DYNAMIC_DRAW);
glBindBuffer(GL_TRANSFORM_FEEDBACK_BUFFER, speedUpdateVBO);
glBufferData(GL_TRANSFORM_FEEDBACK_BUFFER, sizeof(vector3f)*dataW.size(), NULL, GL_DYNAMIC_COPY);
glBindBufferBase(GL_TRANSFORM_FEEDBACK_BUFFER, 0, speedUpdateVBO);
glEnable(GL_RASTERIZER_DISCARD);
glBeginQuery(GL_TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN, query);
printOglError(); //Until this everything OK, I think
glBeginTransformFeedback(GL_POINTS);
printOglError(); //This one prints out Invalid Value
glDrawArrays(GL_POINTS,0,dataW.size());
glEndTransformFeedback();
glEndQuery(GL_TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN);
glDisable(GL_RASTERIZER_DISCARD);
//retrieve updated data
glGetQueryObjectuiv(query, GL_QUERY_RESULT, &count); //count is 0 -> nothing happend
glBindVertexArray(0);
glDisableVertexAttribArray(shader.getAttributeIndex("speed"));
glDeleteQueries(1, &query);
App.Display();
//some other benchmark stuff
}
着色器：垂直
#version 150 core
in vec3 speed;
varying vec3 sp;
const float gravity_constant = 9.81f;
void main(){
sp = speed;
sp += vec3(0,-gravity_constant,0);
}
碎片
#version 150 core
varying vec3 sp;
void main (void)
{
vec3 c = sp;
gl_FragColor = vec4(c,1.0);
}
片段着色器仅用于 GLSL 优化。如果不使用 sp，GLSL 会清除它。可能有一些小错误，因为我从更大的代码中提取了这些错误，其中多个变量也失败了。