OpenGL屏幕外渲染返回清晰的颜色

Question

我有一个简单的函数，它应该接受OpenGL中现有的纹理，并将其调整大小/缩小到给定的宽度和高度，并返回新纹理ID的ID。

它第一次运行时非常好，代码可以在同一源纹理甚至生成的纹理上多次运行（在循环中）。然而，一旦一个帧通过，代码就不再工作了。一旦函数被破坏，结果是具有正确宽度和高度输入的纹理，但是它根本不使用输入纹理，并且输出像素是使用的清晰颜色glClearColor(0, 1, 1, 1);的像素。使用传统的OpenGL代码显示彩色四边形也可以工作一次，然后停止工作，这让我认为问题不在于输入纹理，而是FBO中没有绘制几何体。

GLuint Texture::Downsample(int width, int height, GLuint source)
{
    // Use the largest values
    width = Max(16, width);
    height = Max(16, height);
    // Create a frame buffer object
    GLuint fbo, rbo, target_texture;
    glGenFramebuffers(1, &fbo);
    glBindFramebuffer(GL_FRAMEBUFFER, fbo);
    glGenTextures(1, &target_texture); // Create the target texture
    GLenum status;
    // : Target Texture :
    glBindTexture(GL_TEXTURE_2D, target_texture); // Bind the texture position unit to be used as a buffer
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGBA, GL_UNSIGNED_SHORT, NULL);
    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, target_texture, 0); // Setup the Framebuffer
    status = glCheckFramebufferStatus(GL_FRAMEBUFFER);
    if (status != GL_FRAMEBUFFER_COMPLETE) throw;
    glGenRenderbuffers(1, &rbo);
    glBindRenderbuffer(GL_RENDERBUFFER, rbo);
    glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT, width, height);
    glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, rbo);
    status = glCheckFramebufferStatus(GL_FRAMEBUFFER);
    if (status != GL_FRAMEBUFFER_COMPLETE) throw;
    glBindFramebuffer(GL_FRAMEBUFFER, 0);
    glBindRenderbuffer(GL_RENDERBUFFER, 0);
    glBindTexture(GL_TEXTURE_2D, 0);
    // Use the FBO to draw to the color attachment
    glBindFramebuffer(GL_DRAW_FRAMEBUFFER, fbo);
    glDrawBuffer(GL_COLOR_ATTACHMENT0);
    glPushAttrib(GL_VIEWPORT_BIT | GL_COLOR_BUFFER_BIT);
    glViewport(0, 0, width, height);
    glClearColor(0, 1, 1, 1);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glDisable(GL_DEPTH_TEST);
    // : Draw the original texture
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    //this->Bind(GL_TEXTURE0);
    glEnable(GL_TEXTURE_2D);
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, source);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glDisable(GL_DEPTH_TEST);                                                       // Disable Depth Testing
    glDisable(GL_CULL_FACE);
    // Geometry Data
    const float uvdata[] = { 0.0f, 0.0f, 1.0f, 0.0f, 1.0f, 1.0f, 0.0f, 1.0f };
    const float geometrydata[] = { -1.0f, -1.0f, 0.0f, 1.0f, -1.0f, 0.0f, 1.0f, 1.0f, 0.0f, -1.0f, 1.0f, 0.0f };
    const unsigned char indices[] = { 0, 1, 2, 2, 3, 0 };
    glEnableClientState(GL_VERTEX_ARRAY);                               // Enable Client Vertex Arrays
    glEnableClientState(GL_TEXTURE_COORD_ARRAY);                // Enable Client Texture Coordinate Arrays
    glVertexPointer(3, GL_FLOAT, 0, &geometrydata[0]);      // Pass the geometry data into the Vertex Array
    glTexCoordPointer(2, GL_FLOAT, 0, &uvdata[0]);              // Pass the UV data into the Texture Coordinate Array
    // Draw the geometry using the indices
    glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_BYTE, indices);
    glDisableClientState(GL_TEXTURE_COORD_ARRAY);               // Disable Client Texture Coordinate Arrays
    glDisableClientState(GL_VERTEX_ARRAY);                              // Disable Client Vertex Arrays
    glPopAttrib();
    glDeleteTextures(1, &source); // Delete the old texture
    glDrawBuffer(GL_NONE);
    glBindFramebuffer(GL_FRAMEBUFFER, 0);
    glBindRenderbuffer(GL_RENDERBUFFER, 0);
    glBindTexture(GL_TEXTURE_2D, 0);
    glDeleteFramebuffers(1, &fbo);
    glDeleteRenderbuffers(1, &rbo);
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, target_texture);
    int w, h;
    int miplevel = 0;
    glGetTexLevelParameteriv(GL_TEXTURE_2D, miplevel, GL_TEXTURE_WIDTH, &w);
    glGetTexLevelParameteriv(GL_TEXTURE_2D, miplevel, GL_TEXTURE_HEIGHT, &h);
    return target_texture;
}

Answer 1

找到答案（按照惯例，在我提出问题后10分钟）。我正在运行OpenGL的多上下文实现。因此，在函数返回后立即使用输入纹理ID，但GPU尚未完成处理。

只要在返回之前添加一个glFinish()并创建一个互斥锁场景就很有魅力。然后，当访问纹理时，对互斥体进行try锁定，以确定它是否在使用中。

例如。 Mutex.Instance.lock(); TextureID_Internal = Downsample(128,128, TextureID_Internal); Mutex.Instance.unlock();