关于objective C：渲染到纹理，然后在iOS中渲染纹理到屏幕

Render to texture, then render texture to screen in iOS

我正在尝试将一个简单的场景渲染到一个 FBO 中，该 FBO 由作为颜色附件的纹理支持，然后在 iOS 中使用此纹理在屏幕上绘制一个四边形。
这将帮助我对最终场景进行一些后期处理。 SO上有一些问题可以解决类似(但不完全相同)的问题，我已经尝试了我能理解的任何东西。没有任何效果。

我有两个着色器程序。第一个 _program 简单地获取顶点位置并用单一颜色渲染它们。第二个 quadProgram 采用纹理、纹理坐标和四边形坐标。 (为了简洁起见，我省略了这些着色器的代码。)

两个着色器都能正常工作。他们独立地产生正确的结果。但是，当我尝试将"渲染纹理"渲染到四边形而不是使用样本木材纹理时，我只是得到一个黑屏。这是相关的代码位。我像这样设置一切：

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- (void)setupGL
{
[EAGLContext setCurrentContext:self.context];

_program = [self createProgramWithVertexShader:@"Shader" fragShader:@"Shader"];
GLuint GLKVertexAttribPosition = glGetAttribLocation(_program,"position");

quadProgram = [self createProgramWithVertexShader:@"PostShader" fragShader:@"PostShader"];
quadTexCoord = glGetAttribLocation(quadProgram,"a_texcoord");
quadPosition = glGetAttribLocation(quadProgram,"a_position");
diffuseTexture = glGetUniformLocation(quadProgram,"s_diffuse");

glEnable(GL_DEPTH_TEST);

glGenVertexArraysOES(1, &_vertexArray);
glBindVertexArrayOES(_vertexArray);

glGenBuffers(1, &_vertexBuffer);
glBindBuffer(GL_ARRAY_BUFFER, _vertexBuffer);
glBufferData(GL_ARRAY_BUFFER, sizeof(gCubeVertexData), gCubeVertexData, GL_STATIC_DRAW);

glEnableVertexAttribArray(GLKVertexAttribPosition);
glVertexAttribPointer(GLKVertexAttribPosition, 3, GL_FLOAT, GL_FALSE, 24, BUFFER_OFFSET(0));

glBindVertexArrayOES(0);

// ============
// ---- for render to texture
width = self.view.bounds.size.width;
height = self.view.bounds.size.height;

// create fbo
glGenFramebuffers(1, &framebuffer);
glBindFramebuffer(GL_FRAMEBUFFER, framebuffer);

// create and attach backing texture
glGenTextures(1, &texture);
glBindTexture(GL_TEXTURE_2D, texture);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, texture, 0);

// create and attach depthbuffer
glGenRenderbuffers(1, &depthRenderbuffer);
glBindRenderbuffer(GL_RENDERBUFFER, depthRenderbuffer);
glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT16, width, height);
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, depthRenderbuffer);

// Check if framebuffer was loaded correctly
GLenum status = glCheckFramebufferStatus(GL_FRAMEBUFFER) ;
if(status != GL_FRAMEBUFFER_COMPLETE) {
NSLog(@"failed to make complete framebuffer object %x", status);
}

// sample texture
NSError *theError;

NSString *filePath = [[NSBundle mainBundle] pathForResource:@"wood_floor_256" ofType:@"jpg"]; // 1

spriteTexture = [GLKTextureLoader textureWithContentsOfFile:filePath options:nil error:&theError]; // 2
}

然后是我的主循环：

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- (void)update
{
// First save the default frame buffer.
static GLint default_frame_buffer = 0;
glGetIntegerv(GL_FRAMEBUFFER_BINDING, &default_frame_buffer);

// render to texture
glBindFramebuffer(GL_FRAMEBUFFER, framebuffer);
glClearColor(0.65f, 0.65f, 0.65f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

glBindVertexArrayOES(_vertexArray);

glUseProgram(_program);

glDrawArrays(GL_TRIANGLES, 0, 36);

// render to screen
glBindFramebuffer(GL_FRAMEBUFFER, default_frame_buffer);
glClearColor(0.65f, 0.65f, 0.65f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

glUseProgram(quadProgram);

const float quadPositions[] = { 1.0, 1.0, 0.0,
-1.0, 1.0, 0.0,
-1.0, -1.0, 0.0,
-1.0, -1.0, 0.0,
1.0, -1.0, 0.0,
1.0, 1.0, 0.0 };
const float quadTexcoords[] = { 1.0, 1.0,
0.0, 1.0,
0.0, 0.0,
0.0, 0.0,
1.0, 0.0,
1.0, 1.0 };

// stop using VBO and other bufs.
glBindBuffer(GL_ARRAY_BUFFER, 0);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
glBindVertexArrayOES(0);

glBindTexture(GL_TEXTURE_2D, texture);
glActiveTexture(GL_TEXTURE_2D);

// setup buffer offsets
glVertexAttribPointer(quadPosition, 3, GL_FLOAT, GL_FALSE, 3*sizeof(float), quadPositions);
glVertexAttribPointer(quadTexCoord, 2, GL_FLOAT, GL_FALSE, 2*sizeof(float), quadTexcoords);

// ensure the proper arrays are enabled
glEnableVertexAttribArray(quadPosition);
glEnableVertexAttribArray(quadTexCoord);

// draw
glDrawArrays(GL_TRIANGLES, 0, 2*3);
}

我什至不知道如何判断支持 texture 是否包含渲染的屏幕。

渲染到纹理部分应该渲染到 FBO 中：
iPad render

如果我替换这两行：

1 2	glBindTexture(GL_TEXTURE_2D, texture); glActiveTexture(GL_TEXTURE_2D);

与

1 2	glBindTexture(spriteTexture.target, spriteTexture.name); glEnable(spriteTexture.target);

我得到以下信息：

ipadwood

这表明使用纹理将四边形渲染到屏幕的代码是正确的。

我不知道如何将第一个屏幕渲染到四边形。