iOS:如何在GLES2中渲染到1通道纹理

Question

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RG和B频道.

但是,如果我尝试切换GL_RGBA/**GL_ALPHA /在glTexImage2D,glCheckFramebufferStatus接球"帧缓冲不完整的"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'
    // 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();
}

Answer 1

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

http://developer.apple.com/library/ios/#releasenotes/General/WhatsNewIniPhoneOS/Articles/iOS5.html#//apple_ref/doc/uid/TP30915195-SW47

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.

Answer 2

不，OpenGL ES 2.0 没有任何可渲染的 1 通道纹理格式。GL_ALPHA 和 GL_LUMINANCE 不可渲染，因此它们对 RTT 毫无用处。