OpenGL渲染到纹理看起来参差不齐

我正在使用OpenGL编写一个程序，以在GPU中渲染帧，然后将其传输到内存中，以便可以在其他程序中使用它们。我不需要窗口或渲染到屏幕，因此我正在使用GLFW，但具有隐藏的窗口和上下文。在opengl-tutorial.com之后，我设置了带有纹理和深度渲染缓冲区的帧缓冲区，以便可以渲染到纹理，然后读取其像素。只是为了检查事物，我可以使窗口可见，然后将纹理渲染回屏幕上的四边形并使用直通着色器。

我的问题是，当我直接渲染到屏幕（没有帧缓冲区或纹理）时，图像看起来非常平滑。但是，当我渲染到纹理然后再将纹理渲染到屏幕时，它看起来参差不齐。我不认为问题出在将纹理渲染到屏幕上时，因为我还将将读取的像素保存到.jpg中，并且该像素看上去也呈锯齿状。

窗口和纹理的大小均为512x512像素。

这是我设置帧缓冲区的代码：

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;

这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);
}

其中draw（ShaderProgram）是调用glDrawArrays的函数。这是我将纹理渲染到屏幕上的代码：

// 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);

这是将场景直接渲染到屏幕时得到的：

这是将场景渲染为纹理时得到的：

I can include the code for the vertex and fragment shaders used in rendering the texture to screen, but as I am reading the pixel data straight from the texture and writing it to a file and that still looks jagged, I don't think that is the problem. If there is anything else you want me to include, let me know!

I thought maybe it could be that there is some hidden scaling when doing the rendering to texture and so GL_NEAREST makes it look bad, but if it really is pixel to pixel (both windows and texture are the same size) there shouldn't be a problem there right?