经过数小时的抨击，我现在很确定这是不可能的。
到目前为止，这是我用于渲染纹理的代码（如下）；它可以完成工作，但是非常浪费。我只想要一个 8 位通道，可能是 16 位灰度。我不想要一个无用的 RG 和 B 频道。
但是如果我尝试在 glTexImage2D 中切换 GL_RGBA /*GL_ALPHA*/，glCheckFramebufferStatus 会捕获“帧缓冲区不完整”错误：36054 0x8CD6 GL_FRAMEBUFFER_INCOMPLETE_ATTACHMENT
IRC 上的人建议使用 GL_R，但 Xcode 不为此提供自动完成功能，所以看起来它可能是为 GLES 从 GL 中剪除的东西之一
但这似乎真的很奇怪！这是一个移动设备。当然，可以将执行操作所需的位数减少四倍……当然，这将是最后要做的事情之一。
？！？
谁能彻底埋葬这个？是否可以在 GLES2.0 中渲染到单通道纹理？
+ (void) blurTexture: (GLuint) in_texId
POTWidth: (GLuint) in_W
POTHeight: (GLuint) in_H
returningTexId: (GLuint*) out_pTexId
{
// search HELP: 'Using a Framebuffer Object as a Texture'
// http://stackoverflow.com/questions/3613889/gl-framebuffer-incomplete-attachment-when-trying-to-attach-texture
// Create the destination texture, and attach it to the framebuffer’s color attachment point.
// create the texture
GLuint id_texDest;
{
// fragshader will use 0
glActiveTexture( GL_TEXTURE0 );
// Ask GL to give us a texture-ID for us to use
glGenTextures( 1, & id_texDest );
glBindTexture( GL_TEXTURE_2D, id_texDest );
// actually allocate memory for this texture
GLuint pixCount = in_W * in_H;
typedef struct { uint8_t r, g, b, a } rgba;
rgba * alphas = calloc( pixCount, sizeof( rgba ) );
// XOR texture
int pix=0;
for ( int x = 0; x < in_W; x++ )
{
for ( int y = 0; y < in_H; y++ )
{
//alphas[ pix ].r = (y < 256) ? x^y : 0;
//alphas[ pix ].g = (y < 512) ? 127 : 0;
//alphas[ pix ].b = (y < 768) ? 127 : 0;
alphas[ pix ].a = (y < 512) ? x^y : 0; // half mottled, half black
pix++;
}
}
// set some params on the ACTIVE texture
glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR/*_MIPMAP_LINEAR*/ );
glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR );
glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE );
glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE );
// WRITE/COPY from P into active texture
glTexImage2D( GL_TEXTURE_2D, 0,
GL_RGBA /*GL_ALPHA*/, in_W, in_H, 0,
GL_RGBA /*GL_ALPHA*/,
GL_UNSIGNED_BYTE,
(void *) alphas );
//glGenerateMipmap( GL_TEXTURE_2D );
free( alphas );
glLogAndFlushErrors();
}
GLuint textureFrameBuffer;
{
GLint oldFBO;
glGetIntegerv( GL_FRAMEBUFFER_BINDING, & oldFBO );
// create framebuffer
glGenFramebuffers( 1, & textureFrameBuffer );
glBindFramebuffer( GL_FRAMEBUFFER, textureFrameBuffer );
// attach renderbuffer
glFramebufferTexture2D( GL_FRAMEBUFFER,
GL_COLOR_ATTACHMENT0,
GL_TEXTURE_2D,
id_texDest,
0 );
//glDisable( GL_DEPTH_TEST );
// Test the framebuffer for completeness. This test only needs to be performed when the framebuffer’s configuration changes.
GLenum status = glCheckFramebufferStatus( GL_FRAMEBUFFER ) ;
NSAssert1( status == GL_FRAMEBUFFER_COMPLETE, @"failed to make complete framebuffer object %x", status );
// 36054 0x8CD6 GL_FRAMEBUFFER_INCOMPLETE_ATTACHMENT
// unbind frame buffer
glBindFramebuffer( GL_FRAMEBUFFER, oldFBO );
}
glLogAndFlushErrors();
// clear texture bitmap to backcolor
{
GLint oldFBO;
glGetIntegerv( GL_FRAMEBUFFER_BINDING, & oldFBO );
glBindFramebuffer( GL_FRAMEBUFFER, textureFrameBuffer );
glLogAndFlushErrors();
{
float j = 0.1f;
glClearColor( j, j, j, j );
glLogAndFlushErrors();
glClear( GL_COLOR_BUFFER_BIT );
glLogAndFlushErrors();
}
glBindFramebuffer( GL_FRAMEBUFFER, oldFBO );
}
glDeleteFramebuffers( 1, & textureFrameBuffer );
* out_pTexId = id_texDest;
glLogAndFlushErrors();
}