Question

我想将场景渲染到最初为空的纹理。为此，我使用一个Framebuffer对象，我附加一个空的2d纹理和一个深度缓冲区。设置完毕后，为了测试，我在场景中绘制了一个简单的四边形。每个顶点都有不同的颜色，所以我最终期望纹理中有一个颜色插值的四边形。然后我使用包含四边形的纹理并将其映射到另一个四边形。所以，我在默认的Framebuffer中有一个四边形，它有一个包含彩色四边形的纹理。我希望这不会太混乱......

无论如何，我必须在这里遗漏一些东西，因为我得到的只不过是灰色纹理。我基本上遵循this指令非常简单。但是，我无法弄清楚我在这里缺少什么。如果有人能给我一些线索，我将不胜感激。

由于沃尔特

这是我到目前为止的代码： //创建帧缓冲对象 glGenFramebuffers（1，＆amp; frameBufferObject）;

// create depth buffer
glGenRenderbuffers(1, &depthAttachment);

// create empty texture
int width = 512;
int height = 512;
int numberOfChannels = 3;
GLuint internalFormat = GL_RGB;
GLuint format = GL_RGB;

unsigned char* texels = new unsigned char[width * height * numberOfChannels];

glGenTextures(1, &texture);
glBindTexture(GL_TEXTURE_2D, texture);

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);

glTexImage2D(GL_TEXTURE_2D, 0, internalFormat, width, height, 0, format, GL_UNSIGNED_BYTE, texels);

glGenerateMipmap(GL_TEXTURE_2D);

delete[] texels;
texels = NULL;

// activate & bind empty texture
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, texture);

// attach empty texture to framebuffer object
glBindFramebuffer(GL_FRAMEBUFFER, frameBufferObject);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, texture, 0);

// define render targets (empty texture is at GL_COLOR_ATTACHMENT0)
glDrawBuffers(1, GL_COLOR_ATTACHMENT0);

// attach depth buffer
glBindRenderbuffer(GL_RENDERBUFFER, depthAttachment);
glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT, width, height);
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, depthAttachment);

// use framebuffer object
glBindFramebuffer(GL_FRAMEBUFFER, frameBufferObject);

// draw the colored quad into the initially empty texture
glDisable(GL_CULL_FACE);
glDisable(GL_DEPTH_TEST);

// store attibutes
glPushAttrib(GL_VIEWPORT_BIT | GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

// reset viewport
glViewport(0, 0, width, height);

// make background yellow
glClearColor(1.0f, 1.0f, 0.0f, 1.0f);

// draw quad into texture attached to frame buffer object
glColor4f(1.0f, 1.0f, 1.0f, 1.0f);
glBegin(GL_QUADS);
    glColor4f(1.0f, 1.0f, 1.0f, 1.0f); glVertex2f(0.0f, 100.0f); // top left
    glColor4f(1.0f, 0.0f, 0.0f, 1.0f); glVertex2f(0.0f, 0.0f); // bottom left
    glColor4f(0.0f, 1.0f, 0.0f, 1.0f); glVertex2f(100.0f, 0.0f); // bottom right
    glColor4f(0.0f, 0.0f, 1.0f, 1.0f); glVertex2f(100.0f, 100.0f); // top right
glEnd();

// restore attributes
glPopAttrib();

glEnable(GL_DEPTH_TEST);
glEnable(GL_CULL_FACE);

// use default framebuffer
glBindFramebuffer(GL_FRAMEBUFFER, 0);

// clear default framebuffer
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

// draw the scene
glMatrixMode(GL_MODELVIEW);
glPushMatrix();
glLoadIdentity();

glColor4f(1.0, 1.0, 1.0, 1.0);

// begin texture mapping
glEnable(GL_TEXTURE_2D);
glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);

glBegin(GL_QUADS);
    glNormal3d(0.0f, 0.0f, 1.0f);
    glTexCoord2f(0.0f, 0.0f); glVertex3f(0.0f, 50.0f, -100.0f);    // top left
    glTexCoord2f(0.0f, 1.0f); glVertex3f(0.0f, 0.0f, -100.0f);     // bottom left
    glTexCoord2f(1.0f, 1.0f); glVertex3f(50.0f, 0.0f, -100.0f);    // bottom right
    glTexCoord2f(1.0f, 0.0f); glVertex3f(50.0f, 50.0f, -100.0f);   // top right
glEnd();

glDisable(GL_TEXTURE_2D);

glPopMatrix();

// swap buffers (I forgot to mention that I use SDL)
SDL_GL_SwapBuffers();

预期结果：

黄色背景上带有彩色四边形的纹理
该纹理映射到另一个四元组

实际结果：

灰色纹理
纹理可以成功映射到其他四边形

编辑：我错过了提到错误处理。这是我检查错误的方法。它包括Paul S建议的其他案例。谢谢你。

GLuint status = glCheckFramebufferStatus(GL_FRAMEBUFFER);
switch(status) {
    case GL_FRAMEBUFFER_COMPLETE:
        return;
        break;

case GL_FRAMEBUFFER_INCOMPLETE_ATTACHMENT:
    throw FramebufferIncompleteException("An attachment could not be bound to frame buffer object!");
    break;

case GL_FRAMEBUFFER_INCOMPLETE_MISSING_ATTACHMENT:
    throw FramebufferIncompleteException("Attachments are missing! At least one image (texture) must be bound to the frame buffer object!");
    break;

case GL_FRAMEBUFFER_INCOMPLETE_DIMENSIONS_EXT:
    throw FramebufferIncompleteException("The dimensions of the buffers attached to the currently used frame buffer object do not match!");
    break;

case GL_FRAMEBUFFER_INCOMPLETE_FORMATS_EXT:
    throw FramebufferIncompleteException("The formats of the currently used frame buffer object are not supported or do not fit together!");
    break;

case GL_FRAMEBUFFER_INCOMPLETE_DRAW_BUFFER:
    throw FramebufferIncompleteException("A Draw buffer is incomplete or undefinied. All draw buffers must specify attachment points that have images attached.");
    break;

case GL_FRAMEBUFFER_INCOMPLETE_READ_BUFFER:
    throw FramebufferIncompleteException("A Read buffer is incomplete or undefinied. All read buffers must specify attachment points that have images attached.");
    break;

case GL_FRAMEBUFFER_INCOMPLETE_MULTISAMPLE:
    throw FramebufferIncompleteException("All images must have the same number of multisample samples.");
    break;

case GL_FRAMEBUFFER_INCOMPLETE_LAYER_TARGETS :
    throw FramebufferIncompleteException("If a layered image is attached to one attachment, then all attachments must be layered attachments. The attached layers do not have to have the same number of layers, nor do the layers have to come from the same kind of texture.");
    break;

case GL_FRAMEBUFFER_UNSUPPORTED:
    throw FramebufferIncompleteException("Attempt to use an unsupported format combinaton!");
    break;

default:
    throw FramebufferIncompleteException("Unknown error while attempting to create frame buffer object!");
    break;
}

编辑2：这是我用来检查GL错误的方法

checkForGLErrors(string sourceFile, int line)
    GLenum error = glGetError();
    ostringstream o;

    switch(error) {
        case GL_NO_ERROR:
            return;
            break;

        case GL_INVALID_ENUM:
            o<<"OpenGL Error in "<<sourceFile<<" at line "<<line<<": Invalid enum!"<<endl;
            throw GLErrorException(o.str());
            break;

        case GL_INVALID_VALUE:
            o<<"OpenGL Error in "<<sourceFile<<" at line "<<line<<": Invalid value!"<<endl;
            throw GLErrorException(o.str());
            break;

        case GL_INVALID_OPERATION:
            o<<"OpenGL Error in "<<sourceFile<<" at line "<<line<<": Invalid operation!"<<endl;
            throw GLErrorException(o.str());
            break;

        case GL_STACK_OVERFLOW:
            o<<"OpenGL Error in "<<sourceFile<<" at line "<<line<<": Stack overflow!"<<endl;
            throw GLErrorException(o.str());
            break;

        case GL_STACK_UNDERFLOW:
            o<<"OpenGL Error in "<<sourceFile<<" at line "<<line<<": Stack underflow!"<<endl;
            throw GLErrorException(o.str());
            break;

        case GL_OUT_OF_MEMORY:
            o<<"OpenGL Error in "<<sourceFile<<" at line "<<line<<": Out Of memory!"<<endl;
            throw GLErrorException(o.str());
            break;

        case GL_TABLE_TOO_LARGE:
            o<<"OpenGL Error in "<<sourceFile<<" at line "<<line<<": Table too large!"<<endl;
            throw GLErrorException(o.str());
            break;

        default:
            o<<"OpenGL Error in "<<sourceFile<<" at line "<<line<<": Unknown error!"<<endl;
            throw GLErrorException(o.str());
            break;
    }
}

Answer 1

我解决了这个问题。

所以这就是我的工作。也许有一些更好/更聪明的方法来做到这一点，但它现在完美无缺。随意建议适应...

我没有在下面列出错误处理。你可以在这个问题中找到更多。

// create frame buffer object
glGenFramebuffers(1, frameBufferObject);

// create empty texture
int width = 512;
int height = 512;
int numberOfChannels = 3;
GLuint internalFormat = GL_RGB8;
GLuint format = GL_RGB;

unsigned char* texels = new unsigned char[width * height * numberOfChannels];

glGenTextures(1, &texture);
glBindTexture(GL_TEXTURE_2D, texture);

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);

glTexImage2D(GL_TEXTURE_2D, 0, internalFormat, width, height, 0, format, GL_UNSIGNED_BYTE, texels);

delete[] texels;
texels = NULL;

// draw the colored quad into the initially empty texture
glDisable(GL_CULL_FACE);
glDisable(GL_DEPTH_TEST);

// store attibutes
glPushAttrib(GL_VIEWPORT_BIT | GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

// reset viewport
glViewport(0, 0, width, height);

// setup modelview matrix
glMatrixMode(GL_MODELVIEW);
glPushMatrix();
glLoadIdentity();

// setup projection matrix
glMatrixMode(GL_PROJECTION);
glPushMatrix();
glLoadIdentity();

// setup orthogonal projection
glOrtho(-width / 2, width / 2, -height / 2, height / 2, 0, 1000);

// bind framebuffer object
glBindFramebuffer(GL_FRAMEBUFFER, frameBufferObject);

// attach empty texture to framebuffer object
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, texture, 0);

// check framebuffer status (see above)

// bind framebuffer object (IMPORTANT! bind before adding color attachments!)
glBindFramebuffer(GL_FRAMEBUFFER, frameBufferObject);

// define render targets (empty texture is at GL_COLOR_ATTACHMENT0)
glDrawBuffers(1, GL_COLOR_ATTACHMENT0); // you can of course have more than only 1 attachment

// activate & bind empty texture
// I figured activating and binding must take place AFTER attaching texture as color attachment
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, texture);

// clear color attachments
glClear(GL_COLOR_BUFFER_BIT);

// make background yellow
glClearColor(1.0f, 1.0f, 0.0f, 1.0f);

// draw quad into texture attached to frame buffer object
glColor4f(1.0f, 1.0f, 1.0f, 1.0f);
glBegin(GL_QUADS);
    glColor4f(1.0f, 1.0f, 1.0f, 1.0f); glVertex2f(0.0f, 100.0f); // top left
    glColor4f(1.0f, 0.0f, 0.0f, 1.0f); glVertex2f(0.0f, 0.0f); // bottom left
    glColor4f(0.0f, 1.0f, 0.0f, 1.0f); glVertex2f(100.0f, 0.0f); // bottom right
    glColor4f(0.0f, 0.0f, 1.0f, 1.0f); glVertex2f(100.0f, 100.0f); // top right
glEnd();

// reset projection matrix
glMatrixMode(GL_PROJECTION);
glPopMatrix();

// reset modelview matrix
glMatrixMode(GL_MODELVIEW);
glPopMatrix();

// restore attributes
glPopAttrib();

glEnable(GL_DEPTH_TEST);
glEnable(GL_CULL_FACE);

// I guess, now it's OK to create MipMaps

// draw the scene
glMatrixMode(GL_MODELVIEW);
glPushMatrix();
glLoadIdentity();

glColor4f(1.0, 1.0, 1.0, 1.0);

// begin texture mapping
glEnable(GL_TEXTURE_2D);
    glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);

    // normal faces "camera"
    glNormal3d(0.0f, 0.0f, 1.0f);

    glBegin(GL_QUADS);
        glNormal3d(0.0f, 0.0f, 1.0f);
        glTexCoord2f(0.0f, 0.0f); glVertex3f(0.0f, 50.0f, -100.0f);    // top left
        glTexCoord2f(0.0f, 1.0f); glVertex3f(0.0f, 0.0f, -100.0f);     // bottom left
        glTexCoord2f(1.0f, 1.0f); glVertex3f(50.0f, 0.0f, -100.0f);    // bottom right
        glTexCoord2f(1.0f, 0.0f); glVertex3f(50.0f, 50.0f, -100.0f);   // top right
    glEnd();

glDisable(GL_TEXTURE_2D);

glPopMatrix();

// finish rendering
glFlush();
glFinish();

// swap buffers (I forgot to mention that I use SDL)
SDL_GL_SwapBuffers();

// do the clean up!

如您所见，我摆脱了深度缓冲附件。我认为我并不真的需要它来完成我的任务。一旦我真的可以绘制东西，我就添加了正交投影。没有它，绘制到纹理会导致相当笨拙的图像......

希望这对那里的人有用沃尔特

Answer 2

很奇怪，glDrawBuffers和glFramebufferTexture2D看起来都不像规格！第一个采用GLenum的数组，而不是GLenum（检查警告：它可以静默投放！）。而第二个只在规格上有4个参数！

编辑：

void glDrawBuffers(GLsizei  n,  const GLenum * bufs);

Answer 3

我期待发生的事情：

您正在从未填充的mip-map级别进行渲染。在渲染彩色四边形之前，你正在调用glGenerateMipmap。现在就试试GL_NEAREST。
创建帧缓冲区对象时出现错误。如果发生这种情况，你的渲染就会陷入黑洞。

这是我用来检查帧缓冲区状态的代码片段。它使用EXO版本的FBO并且在Objective-C中（因此是@“”字符串），但它应该是显而易见的。在我调用了glBindFramebuffer，glFramebufferTexture2D＆amp; glDrawBuffers。

    GLenum framebufferStatus = glCheckFramebufferStatusEXT(GL_FRAMEBUFFER_EXT);

    switch (framebufferStatus) {
        case GL_FRAMEBUFFER_COMPLETE_EXT: break;
        case GL_FRAMEBUFFER_INCOMPLETE_ATTACHMENT_EXT:
            NSLog(@"Framebuffer Object %d Error: Attachment Point Unconnected", i);
            break;
        case GL_FRAMEBUFFER_INCOMPLETE_MISSING_ATTACHMENT_EXT:
            NSLog(@"Framebuffer Object %d Error: Missing Attachment", i);
            break;
        case GL_FRAMEBUFFER_INCOMPLETE_DIMENSIONS_EXT:
            NSLog(@"Framebuffer Object %d Error: Dimensions do not match", i);
            break;
        case GL_FRAMEBUFFER_INCOMPLETE_FORMATS_EXT:
            NSLog(@"Framebuffer Object %d Error: Formats", i);
            break;
        case GL_FRAMEBUFFER_INCOMPLETE_DRAW_BUFFER_EXT:
            NSLog(@"Framebuffer Object %d Error: Draw Buffer", i);
            break;
        case GL_FRAMEBUFFER_INCOMPLETE_READ_BUFFER_EXT:
            NSLog(@"Framebuffer Object %d Error: Read Buffer", i);
            break;
        case GL_FRAMEBUFFER_UNSUPPORTED_EXT:
            NSLog(@"Framebuffer Object %d Error: Unsupported Framebuffer Configuration", i);
            break;
        default:
            NSLog(@"Framebuffer Object %d Error: Unkown Framebuffer Object Failure", i);
            break;
    }

问题可能是深度缓冲，因为驱动程序往往对此非常挑剔。对于此测试，您不需要深度，因此如果它导致问题，您可以删除渲染缓冲区内容。

另外需要注意的是，纹理不需要绑定和活动来渲染它。你可以推迟该代码，直到你想用它来渲染你的最终图像。

OpenGL：渲染到纹理的问题＆amp;帧缓冲对象

3 个答案: