GLImageProcessing 多个过滤器？答案

【问题标题】：GLImageProcessing Multiple Filters?GLImageProcessing 多个过滤器？
【发布时间】：2011-09-13 06:05:44
【问题描述】：

我在这里阅读了这个问题：Can example "GLImageProcessing" work with multi filters 但是，我仍然不明白如何编辑 GLImageProcessing 的示例代码以支持多个过滤器。这是我现在在 Imaging.c 的 drawGL 中所做的代码

有什么帮助吗？

void drawGL(int wide, int high, float val, int mode)
{
    GLuint ResultFBO;
    GLuint ResultTexture;
    static int prevmode = -1;
    typedef void (*procfunc)(V2fT2f *, float);

    typedef struct {
        procfunc func;
        procfunc degen;
    } Filter;

    const Filter filter[] = {
        { brightness             },
        { contrast               },
        { extrapolate, greyscale },
        { hue                    },
        { extrapolate, blur      }, // The blur could be exaggerated by downsampling to half size
    };
#define NUM_FILTERS (sizeof(filter)/sizeof(filter[0]))
    rt_assert(mode < NUM_FILTERS);


    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrthof(0, wide, 0, high, -1, 1);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    glScalef(wide, high, 1);

    glBindTexture(GL_TEXTURE_2D, Input.texID);

    // Remember the FBO being used for the display framebuffer
    glGetIntegerv(GL_FRAMEBUFFER_BINDING_OES, (GLint *)&SystemFBO);

    // Create the texture and the FBO the will hold the result of applying the first filter
    glGenTextures(1, &ResultTexture);
    glBindTexture(GL_TEXTURE_2D, ResultTexture);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, wide, high, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
    glGenFramebuffersOES(1, &ResultFBO);
    glBindFramebufferOES(GL_FRAMEBUFFER_OES, ResultFBO);
    glFramebufferTexture2DOES(GL_FRAMEBUFFER_OES, GL_COLOR_ATTACHMENT0_OES, GL_TEXTURE_2D, ResultTexture, 0);

    // bind the result FBO
    glBindFramebufferOES(GL_FRAMEBUFFER_OES, ResultFBO);


    // apply 1st filter
    glViewport(0, 0, wide, high);
    filter[mode].func(flipquad, val);

    // restore original frame buffer object
    glBindFramebufferOES(GL_FRAMEBUFFER_OES, SystemFBO);

    // use ResultTexture as input for the 2nd filter
    glBindTexture(GL_TEXTURE_2D, ResultTexture);

    // apply 2nd filter
    glViewport(0, 0, wide, high);
    filter[2].func(flipquad, val);

    glCheckError();
}

【问题讨论】：

标签： iphone opengl-es filter

【解决方案1】：

您可以通过在两个缓冲区之间交替来扩展此方案：

GLuint stageTextures[2];
glGenTextures(2, stageTextures);

glBindTexture(GL_TEXTURE_2D, stageTexture[0]);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, wide, high, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);

glBindTexture(GL_TEXTURE_2D, stageTexture[1]);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, wide, high, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);

GLuint stageFBO[2];
glGenFramebuffersOES(2, stageFB0);

glBindFramebufferOES(GL_FRAMEBUFFER_OES, stageFBO[0]);
glFramebufferTexture2DOES(GL_FRAMEBUFFER_OES, GL_COLOR_ATTACHMENT0_OES, GL_TEXTURE_2D, stageTexture[0], 0);    

glBindFramebufferOES(GL_FRAMEBUFFER_OES, stageFBO[1]);
glFramebufferTexture2DOES(GL_FRAMEBUFFER_OES, GL_COLOR_ATTACHMENT0_OES, GL_TEXTURE_2D, stageTexture[1], 0);    

// bind stage 1, sourcing stage 0
glBindFramebufferOES(GL_FRAMEBUFFER_OES, stageFBO[1]);
glBindTexture(GL_TEXTURE_2D, stageTexture[0]);

// apply 1st filter
glViewport(0, 0, wide, high);
filter[mode].func(flipquad, val);

glBindTexture(GL_TEXTURE_2D, 0); // must unbind texture before FBO with that texture attached can be bound


// bind stage 0, sourcing stage 1
glBindFramebufferOES(GL_FRAMEBUFFER_OES, stageFBO[0]);
glBindTexture(GL_TEXTURE_2D, stageTexture[1]);

// apply 2nd filter
glViewport(0, 0, wide, high);
filter[mode].func(flipquad, val);

glBindTexture(GL_TEXTURE_2D, 0); // must unbind texture before FBO with that texture attached can be bound

// bind stage 1, sourcing stage 0
glBindFramebufferOES(GL_FRAMEBUFFER_OES, stageFBO[1]);
glBindTexture(GL_TEXTURE_2D, stageTexture[0]);

// apply 3rd filter
glViewport(0, 0, wide, high);
filter[mode].func(flipquad, val);

glBindTexture(GL_TEXTURE_2D, 0); // must unbind texture before FBO with that texture attached can be bound

// and so on. finally

// Bind SystemFBO so the screen is the target, sourcing stage 0/1
// (depending on if a even or odd number of filters involved)
glBindFramebufferOES(GL_FRAMEBUFFER_OES, SystemFBO);
glBindTexture(GL_TEXTURE_2D, stageTexture[...]); // set to follow the scheme above

// apply n-th filter
glViewport(0, 0, wide, high);
filter[mode].func(flipquad, val);

【讨论】：

那么这到底会去哪里呢？我用你的代码替换了从“//记住用于显示帧缓冲区的FBO”开始的所有内容，但仍然没有运气。
在最后一步中，您当然必须绘制到屏幕上，而不是帧缓冲区。我编辑了那个代码示例。
@Flipper：我能想到很多事情。您可以看到某些东西的事实意味着过滤器链正在工作。现在您可能会遇到一些不幸的过滤器组合和排序。由于我手头既没有 iOS 设备也没有模拟器，所以很难重现。
@Flipper：我真的不知道。那些代码 sn-ps 也不包含实际的过滤器代码，它们只是引用了一些函数。如果您也添加这些内容，或者至少提供一个 URL，我可以在其中获取您调整的原始代码，那就太好了。然后我可以将它移植到基于 PC 的 OpenGL 上并对此进行测试。
@Flipper：原始代码使用辅助辅助纹理，在您的代码 sn-p(s) 中不可见。这改变了要采取的整个方法！给我一些时间将该程序移植到我的系统并进行修改。

【解决方案2】：

我能够组合多个过滤器，这是基于此处提出的建议的完整方法。

void drawGL(int wide, int high, float val, int mode)
{

    static int prevmode = -1;
    typedef void (*procfunc)(V2fT2f *, float);

    typedef struct {
            procfunc func;
            procfunc degen;
    } Filter;

    const Filter filter[] = {
            { brightness             },
            { contrast               },
            { extrapolate, greyscale },
            { hue                    },
            { extrapolate, blur      },        // The blur could be exaggerated by downsampling to half size
    };
    #define NUM_FILTERS (sizeof(filter)/sizeof(filter[0]))
    rt_assert(mode < NUM_FILTERS);

    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrthof(0, wide, 0, high, -1, 1);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    glScalef(wide, high, 1);

glGetIntegerv(GL_FRAMEBUFFER_BINDING_OES, (GLint *)&SystemFBO);
// Create the texture and the FBO the will hold the result of applying the first filter
glGenTextures(1, &ResultTexture.texID);
glBindTexture(GL_TEXTURE_2D, ResultTexture.texID);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, wide, high, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
glGenFramebuffersOES(1, &ResultTextureFBO);
glBindFramebufferOES(GL_FRAMEBUFFER_OES, ResultTextureFBO);
glFramebufferTexture2DOES(GL_FRAMEBUFFER_OES, GL_COLOR_ATTACHMENT0_OES, GL_TEXTURE_2D, ResultTexture.texID, 0);

glBindFramebufferOES(GL_FRAMEBUFFER_OES, ResultTextureFBO);
glBindTexture(GL_TEXTURE_2D, Input.texID);

    glViewport(0, 0, wide, high);
brightness(flipquad, val);
    glCheckError();

glBindFramebufferOES(GL_FRAMEBUFFER_OES, SystemFBO);
glBindTexture(GL_TEXTURE_2D, ResultTexture.texID);

    glViewport(0, 0, wide, high);
hue(fullquad, val);
    glCheckError();    
}

【讨论】：