[游戏开发]OpenGL C++渲染到纹理的步骤（部分）

创建顶点缓冲

创建纹理

步骤：创建一个纹理、绑定、填充、配置。

// 首先创建一个OpenGL纹理
GLuint textureID;
glGenTextures(1, &textureID);

//将纹理和对应的ID绑定
glBindTexture(GL_TEXTURE_2D, textureID);

//将图片传到OpenGL中，GL_RGB表示颜色由三个分量构成，GL_BGR则说明了颜色在内存中的存储格式。实际上，BMP存储的并不是RGB，而是BGR，因此得把这个告诉OpenGL。
glTexImage2D(GL_TEXTURE_2D, 0,GL_RGB, width, height, 0, GL_BGR, GL_UNSIGNED_BYTE, data);

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);

利用GLFW加载纹理

GLuint loadTGA_glfw(const char * imagepath){

    // Create one OpenGL texture
    GLuint textureID;
    glGenTextures(1, &textureID);

    // "Bind" the newly created texture : all future texture functions will modify this texture
    glBindTexture(GL_TEXTURE_2D, textureID);

    // Read the file, call glTexImage2D with the right parameters
    glfwLoadTexture2D(imagepath, 0);

    // Nice trilinear filtering.
    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_MAG_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
    glGenerateMipmap(GL_TEXTURE_2D);

    // Return the ID of the texture we just created
    return textureID;
}

渲染到纹理

创建渲染纹理对象

要渲染的对象叫帧缓存。帧缓存是一个包含纹理和深度缓存（可选择）区的容器。 其创建方式与其余的在OpenGL创建对象的方式一致。

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

// The texture we're going to render to
GLuint renderedTexture;
glGenTextures(1, &renderedTexture);

// "Bind" the newly created texture : all future texture functions will modify this texture
glBindTexture(GL_TEXTURE_2D, renderedTexture);

// Give an empty image to OpenGL ( the last "0" )
glTexImage2D(GL_TEXTURE_2D, 0,GL_RGB, 1024, 768, 0,GL_RGB, GL_UNSIGNED_BYTE, 0);

// Poor filtering. Needed !
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);

// 深度缓存
GLuint depthrenderbuffer;
glGenRenderbuffers(1, &depthrenderbuffer);
glBindRenderbuffer(GL_RENDERBUFFER, depthrenderbuffer);
glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT, 1024, 768);
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, depthrenderbuffer);

//把纹理配置到帧缓存中
// Set "renderedTexture" as our colour attachement #0
glFramebufferTexture(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, renderedTexture, 0);

// Set the list of draw buffers.
GLenum DrawBuffers[1] = {GL_COLOR_ATTACHMENT0};
glDrawBuffers(1, DrawBuffers); // "1" is the size of DrawBuffers

把图像渲染到纹理上

渲染纹理很简单。简单地绑定你的帧缓冲区，并像往常一样绘制场景。

// 把图像渲染到帧缓存
glBindFramebuffer(GL_FRAMEBUFFER, FramebufferName);
glViewport(0,0,1024,768); // Render on the whole framebuffer, complete from the lower left corner to the upper right

CUDA和OpenGL互操作

简要说一下如何使CUDA和OpenGL互操作来实现GPU中数据的交互传输，而不用通过主机的CPU。

在OpenGL中声明一个buffer

// 声明一个buffer
cudaGraphicsResource_t  cudaBuffer;
// 将buffer注册给纹理texture
cudaGraphicsGLRegisterImage(&cudaBuffer, texture, GL_TEXTURE_2D, cudaGraphicsRegisterFlagsWriteDiscard);

把CUDA计算出来的数据写入cudaBuffer中

// 利用Cuda中的两个API设置cudaBuffer为映射Map，并将一个cuda数组cudaArray绑定到cudaBuffer。
cudaError_t err;
err = cudaGraphicsMapResources(1, cudaBuffer, 0);  
err = cudaGraphicsSubResourceGetMappedArray(&cudaArray, cudaBuffer, 0, 0);
// 把数据写入cudaArray中，假设我有一个数据指针pResult指向GPU中的一段内存，这段内存中保存的就是CUDA的运算结果(一幅4通道图像)，我只需要将其copy到cudaArray就行了。注意是cudaMemcpyDeviceToDevice
uchar* cudaArray=NULL;
cudaChannelFormatDesc cuDesc = cudaCreateChannelDesc<uchar4>();
cudaMallocArray(&cudaArray, &cuDesc, imgWidth, imgHeight);

// 将结果数据拷贝到cudaArray
err=cudaMemcpyToArray(cudaArray, 0, 0, pResult, imgWidth*imgHeight * sizeof(uchar4), cudaMemcpyDeviceToDevice);
// 拷贝完数据后解除映射map
cudaGraphicsUnmapResources(1, &cudaBuffer, 0);