iOS：如何在GLES2中渲染到1通道纹理

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();
}