OpenGL渲染纹理看起来很锯齿

2018-05-31 00:36:00

我正在用OpenGL制作一个程序，在GPU中渲染帧，然后将其传输到内存中，以便我可以在另一个程序中使用它们。我不需要窗口或渲染器来显示，所以我使用GLFW，但是有一个隐藏的窗口和上下文。在opengl-tutorial.com之后，我设置了一个带有纹理和深度渲染缓冲区的Framebuffer，这样我就可以渲染纹理，然后读取它的像素。只是为了检查一些东西，我可以使窗口可见，并将纹理渲染回四边形的屏幕上，并使用直通着色器。

我的问题是，当我直接渲染到屏幕（没有Framebuffer或纹理）时，图像看起来非常平滑。但是，当我渲染纹理并将纹理渲染到屏幕上时，它看起来很锯齿。我不认为问题是将纹理渲染到屏幕上时，因为我也将我读取的像素保存为.jpg，并且它看起来也是锯齿状的。

窗口和纹理的大小都是512x512像素。

这里是我设置framebuffer的代码：

FramebufferName = 0;
glGenFramebuffers(1, &FramebufferName);
glBindFramebuffer(GL_FRAMEBUFFER, FramebufferName);

//GLuint renderedTexture;
glGenTextures(1, &renderedTexture);
glBindTexture(GL_TEXTURE_2D, renderedTexture);
glTexImage2D(GL_TEXTURE_2D, 0, textureFormat, textureWidth, textureHeight, 0, textureFormat, GL_UNSIGNED_BYTE, 0);

numBytes = textureWidth * textureHeight * 3; // RGB
pixels = new unsigned char[numBytes]; // allocate image data into RAM

glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameterf(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);

//GLuint depthrenderbuffer;
glGenRenderbuffers(1, &depthrenderbuffer);
glBindRenderbuffer(GL_RENDERBUFFER, depthrenderbuffer);
glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT, textureWidth, textureHeight);
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, depthrenderbuffer);

glFramebufferTexture(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, renderedTexture, 0);

DrawBuffers[0] = GL_COLOR_ATTACHMENT0;
glDrawBuffers(1, DrawBuffers); // "1" is the size of DrawBuffers

if(glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE) {
    std::cout << "Couldn't set up frame buffer" << std::endl;
}

g_quad_vertex_buffer_data.push_back(-1.0f);
g_quad_vertex_buffer_data.push_back(-1.0f);
g_quad_vertex_buffer_data.push_back(0.0f);

g_quad_vertex_buffer_data.push_back(1.0f);
g_quad_vertex_buffer_data.push_back(-1.0f);
g_quad_vertex_buffer_data.push_back(0.0f);

g_quad_vertex_buffer_data.push_back(-1.0f);
g_quad_vertex_buffer_data.push_back(1.0f);
g_quad_vertex_buffer_data.push_back(0.0f);

g_quad_vertex_buffer_data.push_back(-1.0f);
g_quad_vertex_buffer_data.push_back(1.0f);
g_quad_vertex_buffer_data.push_back(0.0f);

g_quad_vertex_buffer_data.push_back(1.0f);
g_quad_vertex_buffer_data.push_back(-1.0f);
g_quad_vertex_buffer_data.push_back(0.0f);

g_quad_vertex_buffer_data.push_back(1.0f);
g_quad_vertex_buffer_data.push_back(1.0f);
g_quad_vertex_buffer_data.push_back(0.0f);

//GLuint quad_vertexbuffer;
glGenBuffers(1, &quad_vertexbuffer);
glBindBuffer(GL_ARRAY_BUFFER, quad_vertexbuffer);
glBufferData(GL_ARRAY_BUFFER, g_quad_vertex_buffer_data.size() * sizeof(GLfloat), &g_quad_vertex_buffer_data[0], GL_STATIC_DRAW);

// PBOs
glGenBuffers(cantPBOs, pboIds);
for(int i = 0; i < cantPBOs; ++i) {
    glBindBuffer(GL_PIXEL_PACK_BUFFER, pboIds[i]);
    glBufferData(GL_PIXEL_PACK_BUFFER, numBytes, 0, GL_DYNAMIC_READ);
}
glBindBuffer(GL_PIXEL_PACK_BUFFER, 0);

index = 0;
nextIndex = 0;

以下是我渲染到纹理的代码：

glBindFramebuffer(GL_FRAMEBUFFER, FramebufferName);
glViewport(0,0,textureWidth,textureHeight); // Render on the whole framebuffer, complete from the lower left corner to the upper right

// Clear the screen
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

for(int i = 0; i < geometriesToDraw.size(); ++i) {
    geometriesToDraw[i]->draw(program);
}

draw（ShaderProgram）是调用glDrawArrays的函数。这里是我渲染纹理到屏幕的代码：

// Render to the screen
glBindFramebuffer(GL_FRAMEBUFFER, 0);
// Render on the whole framebuffer, complete from the lower left corner to the upper right
glViewport(0,0,textureWidth,textureHeight);

// Clear the screen
glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glUseProgram(shaderTexToScreen.getProgramID());

// Bind our texture in Texture Unit 0
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, renderedTexture);
// Set our "renderedTexture" sampler to user Texture Unit 0
glUniform1i(shaderTexToScreen.getUniformLocation("renderedTexture"), 0);

// 1rst attribute buffer : vertices
glEnableVertexAttribArray(0);
glBindBuffer(GL_ARRAY_BUFFER, quad_vertexbuffer);
glVertexAttribPointer(
    0,                  
    3,                  
    GL_FLOAT,           
    GL_FALSE,           
    0,                  
    (void*)0            
);

glDrawArrays(GL_TRIANGLES, 0, 6);
glDisableVertexAttribArray(0);

这是我直接渲染场景时所得到的结果：

这是我将场景渲染到纹理时所得到的结果：

我可以包含用于渲染纹理的顶点和片段着色器的代码，但是当我直接从纹理中读取像素数据并将其写入文件并且看起来仍然锯齿状时，我不认为这是问题。如果还有什么你想让我包括，让我知道！

我认为也许这可能是因为渲染纹理时存在一些隐藏的缩放，所以GL_NEAREST使它看起来不好，但如果它真的是像素到像素（窗口和纹理都是相同的大小），应该不会有问题在那里吗？

正如genpfault和Frischer Hering所指出的那样，渲染到正常纹理时没有抗锯齿功能。但是，您可以渲染为多重采样纹理，该纹理将根据您的请求保存尽可能多的样本的信息。要将其渲染为屏幕，您需要对纹理进行采样以获取每个像素的一种颜色，可以通过调用glBlitFramebuffer来完成。根据glBlitFramebuffer上的OpenGL参考：

如果读取帧缓冲区的SAMPLE_BUFFERS大于零，并且绘制帧缓冲区的SAMPLE_BUFFERS为零，则与源中每个像素位置对应的样本在写入目标之前会转换为单个样本。

这两个链接也非常有帮助：

http://www.learnopengl.com/#!Advanced-OpenGL/Anti-alasing http://ake.in.th/2013/04/02/offscreening-and-multisampling-with-opengl/

这是我的解决方案，创建对象：

/// FRAMEBUFFER MULTISAMPLE

framebufferMS = 0;
glGenFramebuffers(1, &framebufferMS);
glBindFramebuffer(GL_FRAMEBUFFER, framebufferMS);

glGenTextures(1, &renderedTextureMS);
glBindTexture(GL_TEXTURE_2D_MULTISAMPLE, renderedTextureMS);
glTexImage2DMultisample(GL_TEXTURE_2D_MULTISAMPLE, SAMPLES, textureFormat, textureWidth, textureHeight, GL_TRUE);

glGenRenderbuffers(1, &depthrenderbufferMS);
glBindRenderbuffer(GL_RENDERBUFFER, depthrenderbufferMS);
glRenderbufferStorageMultisample(GL_RENDERBUFFER, SAMPLES, GL_DEPTH24_STENCIL8, textureWidth, textureHeight);
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, depthrenderbufferMS);

glFramebufferTexture(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, renderedTextureMS, 0);
DrawBuffersMS[0] = GL_COLOR_ATTACHMENT0;
glDrawBuffers(1, DrawBuffersMS);

if(glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE) {
    std::cout << "Couldn't set up frame buffer" << std::endl;
}

/// FRAMEBUFFER SIMPLE

framebuffer = 0;
glGenFramebuffers(1, &framebuffer);
glBindFramebuffer(GL_FRAMEBUFFER, framebuffer);

glGenTextures(1, &renderedTexture);
glBindTexture(GL_TEXTURE_2D, renderedTexture);
glTexImage2D(GL_TEXTURE_2D, 0, textureFormat, textureWidth, textureHeight, 0, textureFormat, GL_UNSIGNED_BYTE, 0);

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

glFramebufferTexture(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, renderedTexture, 0);
DrawBuffers[0] = GL_COLOR_ATTACHMENT0;
glDrawBuffers(1, DrawBuffers); // "1" is the size of DrawBuffers

if(glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE) {
    std::cout << "Couldn't set up frame buffer" << std::endl;
}

渲染过程：

// Render to framebuffer multisample
glBindFramebuffer(GL_FRAMEBUFFER, framebufferMS);
glViewport(0,0,textureWidth,textureHeight);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

for(int i = 0; i < geometriesToDraw.size(); ++i) {
    geometriesToDraw[i]->draw(program);
}

// Sample to normal texture
glBindFramebuffer(GL_READ_FRAMEBUFFER, framebufferMS);
glBindFramebuffer(GL_DRAW_FRAMEBUFFER, framebuffer);
glBlitFramebuffer(0, 0, textureWidth, textureHeight, 0, 0, textureWidth, textureHeight, GL_COLOR_BUFFER_BIT, GL_NEAREST);

你也可以在这里找到关于这个问题的更多问题，我错过了，因为我搜索像“锯齿状”而不是多重采样的术语：P

非常感谢你的帮助！

链接地址: http://www.djcxy.com/p/5821.html

上一篇: OpenGL rendering to texture looks jagged

下一篇: lwjgl and render to texture