我非常肯定,经过几个小时的抨击,这是无法做到的.
到目前为止,这是我的代码(下图),用于渲染纹理;它完成了这项工作,但非常浪费.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R G和B频道.
但是如果我尝试在glTexImage2D中切换GL_RGBA / * GL_ALPHA * /,glCheckFramebufferStatus会捕获’frame buffer incomplete’错误：36054 0x8CD6 GL_FRAMEBUFFER_INCOMPLETE_ATTACHMENT
IRC上的人建议使用GL_R,但是Xcode不提供自动完成功能,所以看起来它可能是GL为GLES修剪过的东西之一
但这似乎很奇怪！这是一个移动设备.当然,将执行操作所需的位数减少了四倍……这肯定是最后要采取的事情之一.
？！？
任何人都可以明确地埋葬这个吗？是否可以在GLES2.0中渲染到单个通道纹理？
+ (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'
// https://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,GL_RGBA /*GL_ALPHA*/,in_W,in_H,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 );
glLogAndFlushErrors();
glClear( GL_COLOR_BUFFER_BIT );
glLogAndFlushErrors();
}
glBindFramebuffer( GL_FRAMEBUFFER,oldFBO );
}
glDeleteFramebuffers( 1,& textureFrameBuffer );
* out_pTexId = id_texDest;
glLogAndFlushErrors();
}
解决方法
从iOS 5.0开始,您可以使用GL_EXT_texture_rg渲染到1和2通道纹理.
http://www.khronos.org/registry/gles/extensions/EXT/EXT_texture_rg.txt
编辑：我已经测试了这个并且它可以工作,但仅适用于A5及以上(iPad2 / 3/4 / mini,iPhone4S / 5,iPod touch第5代).不幸的是,在最需要的地方(iPhone4,iPod touch第4代,3GS,iPad1),它不适用于A4及更老版本.
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