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我有一個非常特定的OpenGL設置，場景中的3D幾何體未呈現。在OpenGL上下文中有一些與深度相關的狀態可以解釋我。使用共享上下文進行渲染時，OpenGL深度緩衝區或深度測試不起作用
這是在工作中的生產引擎中，我們添加了具有多個窗口上下文的共享上下文支持。我們正在對共享上下文擁有的幀緩衝區對象進行渲染，然後使用不同的上下文將顏色附件渲染緩衝區blitting到窗口。
清除顏色顯示在窗口的結果blit中，但不是3D場景幾何本身，所以我們知道幀緩衝區和渲染緩衝區對象至少部分是正確的。
爲了說明，我重構了一個LearnOpenGL網站的示例來說明我的錯誤。它也出現在那裏，所以我很清楚這是我錯過的東西。
這裏是GitHub的項目中，我提出三個提交到工作幀緩衝樣品使之能夠使用共享上下文渲染到幀緩衝區，然後位塊傳輸的結果：Framebuffer Shared Context Experiment
這裏是最能產生的源代碼的越野車的結果。我剪掉了一些沒有改變的部分。
// glfw dummy window creation
// --------------------
GLFWwindow* dummy = NULL;
#if USE_SHARED_CONTEXT
dummy = glfwCreateWindow(1, 1, "Dummy", NULL, NULL);
if (dummy == NULL)
{
std::cout << "Failed to create dummy GLFW window" << std::endl;
glfwTerminate();
return -1;
}
glfwMakeContextCurrent(dummy);
#endif
// glfw window creation
// --------------------
GLFWwindow* window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "LearnOpenGL", NULL, dummy);
if (window == NULL)
{
std::cout << "Failed to create GLFW window" << std::endl;
glfwTerminate();
return -1;
}
glfwShowWindow(window);
#if !USE_SHARED_CONTEXT
glfwMakeContextCurrent(window);
#endif
// <snip creation of shared resources>
// <snip creation of un-shared vertex array>
// framebuffer configuration
// -------------------------
unsigned int framebuffer;
glGenFramebuffers(1, &framebuffer);
glBindFramebuffer(GL_FRAMEBUFFER, framebuffer);
#if 1
// create a color attachment render buffer
unsigned int Colorbuffer;
glGenRenderbuffers(1, &Colorbuffer);
glBindRenderbuffer(GL_RENDERBUFFER, Colorbuffer);
glRenderbufferStorage(GL_RENDERBUFFER, GL_RGBA8, SCR_WIDTH, SCR_HEIGHT); // use a single renderbuffer object for both a depth AND stencil buffer.
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, Colorbuffer); // now actually attach it
#else
// create a color attachment texture
unsigned int textureColorbuffer;
glGenTextures(1, &textureColorbuffer);
glBindTexture(GL_TEXTURE_2D, textureColorbuffer);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, SCR_WIDTH, SCR_HEIGHT, 0, GL_RGB, GL_UNSIGNED_BYTE, NULL);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, textureColorbuffer, 0);
#endif
// create a renderbuffer object for depth and stencil attachment (we won't be sampling these)
unsigned int rbo;
glGenRenderbuffers(1, &rbo);
glBindRenderbuffer(GL_RENDERBUFFER, rbo);
glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH24_STENCIL8, SCR_WIDTH, SCR_HEIGHT); // use a single renderbuffer object for both a depth AND stencil buffer.
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_STENCIL_ATTACHMENT, GL_RENDERBUFFER, rbo); // now actually attach it
// now that we actually created the framebuffer and added all attachments we want to check if it is actually complete now
if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
cout << "ERROR::FRAMEBUFFER:: Framebuffer is not complete!" << endl;
glBindFramebuffer(GL_FRAMEBUFFER, 0);
// render loop
// -----------
while (!glfwWindowShouldClose(window))
{
// <snip timing and input>
#if USE_SHARED_CONTEXT
// use shared context because that is what is holding our framebuffer and vao.
// -----
glfwMakeContextCurrent(dummy);
#endif
// render
// ------
// bind to framebuffer and draw scene as we normally would to color texture
glBindFramebuffer(GL_FRAMEBUFFER, framebuffer);
glEnable(GL_DEPTH_TEST); // enable depth testing (is disabled for rendering screen-space quad)
// make sure we clear the framebuffer's content
glClearColor(1.0f, 0.1f, 0.1f, 1.0f);
glClearDepth(1.0f);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
// following render is unchanged
shader.use();
glm::mat4 model;
glm::mat4 view = camera.GetViewMatrix();
glm::mat4 projection = glm::perspective(camera.Zoom, (float)SCR_WIDTH/(float)SCR_HEIGHT, 0.1f, 100.0f);
shader.setMat4("view", view);
shader.setMat4("projection", projection);
// cubes
glBindVertexArray(cubeVAO);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, cubeTexture);
model = glm::translate(model, glm::vec3(-1.0f, 0.0f, -1.0f));
shader.setMat4("model", model);
glDrawArrays(GL_TRIANGLES, 0, 36);
model = glm::mat4();
model = glm::translate(model, glm::vec3(2.0f, 0.0f, 0.0f));
shader.setMat4("model", model);
glDrawArrays(GL_TRIANGLES, 0, 36);
// floor
glBindVertexArray(planeVAO);
glBindTexture(GL_TEXTURE_2D, floorTexture);
shader.setMat4("model", glm::mat4());
glDrawArrays(GL_TRIANGLES, 0, 6);
glBindVertexArray(0);
#if 1
#if USE_SHARED_CONTEXT
// use window context for presentation via blit.
// -----
glfwMakeContextCurrent(window);
// temorary framebuffer for visible window since framebuffers are not shared
// -------------------------
unsigned int readFramebuffer;
glGenFramebuffers(1, &readFramebuffer);
glBindFramebuffer(GL_READ_FRAMEBUFFER, readFramebuffer);
glBindRenderbuffer(GL_RENDERBUFFER, Colorbuffer);
glRenderbufferStorage(GL_RENDERBUFFER, GL_RGBA8, SCR_WIDTH, SCR_HEIGHT);
glFramebufferRenderbuffer(GL_READ_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, Colorbuffer);
#endif
glBindFramebuffer(GL_DRAW_FRAMEBUFFER, 0);
glBlitFramebuffer(0, 0, SCR_WIDTH, SCR_HEIGHT, 0, 0, SCR_WIDTH, SCR_HEIGHT, GL_COLOR_BUFFER_BIT, GL_NEAREST);
#if USE_SHARED_CONTEXT
glDeleteFramebuffers(1, &readFramebuffer);
#endif
#else
// now bind back to default framebuffer and draw a quad plane with the attached framebuffer color texture
glBindFramebuffer(GL_FRAMEBUFFER, 0);
glDisable(GL_DEPTH_TEST); // disable depth test so screen-space quad isn't discarded due to depth test.
// clear all relevant buffers
glClearColor(1.0f, 1.0f, 1.0f, 1.0f); // set clear color to white (not really necessery actually, since we won't be able to see behind the quad anyways)
glClear(GL_COLOR_BUFFER_BIT);
screenShader.use();
glBindVertexArray(quadVAO);
glBindTexture(GL_TEXTURE_2D, textureColorbuffer); // use the color attachment texture as the texture of the quad plane
glDrawArrays(GL_TRIANGLES, 0, 6);
#endif
// glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.)
// -------------------------------------------------------------------------------
glfwSwapBuffers(window);
glfwPollEvents();
}
// <snip epilog>
您可以切換USE_SHARED_CONTEXT編譯時開關刪除的代碼點點呈現使用共享的上下文。