例如「GLImageProcessing」可以使用多個濾鏡

Question

我使用GLImageProcessing的例子，但它不能處理圖像的亮度和對比度，所以我編寫代碼來調整亮度和對比度，但它不能工作總之，可有人能幫助我這個，感謝您的評論

//init 
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); 


//bind result fbo 
glBindFramebufferOES(GL_FRAMEBUFFER_OES, resultFBO); 
glViewport(0, 0, result.wide*result.s, result.high*result.t); 
glClear(GL_COLOR_BUFFER_BIT); 
glDisable(GL_BLEND); 



//process 1 adjust brightness 
float t = 1.2; 
glVertexPointer (2, GL_FLOAT, sizeof(V2fT2f), &flipquad[0].x); 
glTexCoordPointer(2, GL_FLOAT, sizeof(V2fT2f), &flipquad[0].s); 
glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE); 

static GLfloat constColor[4] = { 0.1, 0.2, 0.3, 0.4 }; 
if (t > 1.0f) 
{ 
    glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_RGB,  GL_ADD); 
    //glColor4f(t-1, t-1, t-1, t-1); 
    constColor[0] = t-1; 
    constColor[1] = t-1; 
    constColor[2] = t-1; 
    constColor[3] = t-1; 
} 
else 
{ 
    glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_RGB,  GL_SUBTRACT); 
    constColor[0] = 1-t; 
    constColor[1] = 1-t; 
    constColor[2] = 1-t; 
    constColor[3] = 1-t; 
} 


glTexEnvfv(GL_TEXTURE_ENV, GL_TEXTURE_ENV_COLOR, constColor); 

glTexEnvi(GL_TEXTURE_ENV, GL_SRC0_RGB,   GL_TEXTURE); 
glTexEnvi(GL_TEXTURE_ENV, GL_SRC1_RGB,   GL_CONSTANT); 
glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_ALPHA, GL_REPLACE); 
glTexEnvi(GL_TEXTURE_ENV, GL_SRC0_ALPHA,  GL_TEXTURE); 


//process 2 adjust contrast 
t = 1.6; 
GLfloat h = t*0.5f; 

// One pass using two units: 
// contrast < 1.0 interpolates towards grey 
// contrast > 1.0 extrapolates away from grey 
// 
// Here, the general extrapolation 2*(Src*t + Dst*(0.5-t)) 
// can be simplified, because Dst is a constant (grey). 
// That results in: 2*(Src*t + 0.25 - 0.5*t) 
// 
// Unit0 calculates Src*t 
// Unit1 adds 0.25 - 0.5*t 
// Since 0.5*t will be in [0..0.5], it can be biased up and the addition done in signed space. 
glActiveTexture(GL_TEXTURE1); 
glEnable(GL_TEXTURE_2D); 
//glVertexPointer (2, GL_FLOAT, sizeof(V2fT2f), &flipquad[0].x); 
//glTexCoordPointer(2, GL_FLOAT, sizeof(V2fT2f), &flipquad[0].s); 
glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE); 
glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_RGB,  GL_MODULATE); 
glTexEnvi(GL_TEXTURE_ENV, GL_SRC0_RGB,   GL_PREVIOUS); 
glTexEnvi(GL_TEXTURE_ENV, GL_SRC1_RGB,   GL_PRIMARY_COLOR); 
glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_ALPHA, GL_REPLACE); 
glTexEnvi(GL_TEXTURE_ENV, GL_SRC0_ALPHA,  GL_PREVIOUS); 


glDisable(GL_TEXTURE_2D); 
glActiveTexture(GL_TEXTURE2); 
glEnable(GL_TEXTURE_2D); 
glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE); 
glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_RGB,  GL_ADD_SIGNED); 
glTexEnvi(GL_TEXTURE_ENV, GL_SRC0_RGB,   GL_PREVIOUS); 
glTexEnvi(GL_TEXTURE_ENV, GL_SRC1_RGB,   GL_PRIMARY_COLOR); 
glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND1_RGB,  GL_SRC_ALPHA); 
glTexEnvi(GL_TEXTURE_ENV, GL_RGB_SCALE,  2); 
glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_ALPHA, GL_REPLACE); 
glTexEnvi(GL_TEXTURE_ENV, GL_SRC0_ALPHA,  GL_PREVIOUS); 

glColor4f(h, h, h, 0.75 - 0.5 * h); // 2x extrapolation 
validateTexEnv(); 
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4); 

//save to file 
snapshot(result,"/test3.jpg"); 

// Restore state 
glDisable(GL_TEXTURE_2D); 
glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND1_RGB,  GL_SRC_COLOR); 
glTexEnvi(GL_TEXTURE_ENV, GL_RGB_SCALE,  1); 
glActiveTexture(GL_TEXTURE0); 
//process 3 adjust hue 

//process 4 mask 

//save to buffer 

//bind system rbo 
glBindFramebufferOES(GL_FRAMEBUFFER_OES, SystemFBO); 
glCheckError(); 

Answer 1

使用多重紋理，它應該能夠找到解決這一問題，會做的伎倆在一通。不幸的是，第一款iPhone的PowerVR MBX GPU僅具有2個紋理單元（OpenGL ES 1.1標準所要求的最低限度），這不足以應用這兩種濾鏡。我認爲更新的硬件最多可以擁有八個紋理單元，並且可以找到單通解決方案。

一個更通用的方法，可以讓你根據需要應用盡可能多的過濾器，就是使用幀緩衝區對象來逐字「渲染到紋理」。這裏是另一篇文章的鏈接，概述了該技術：OpenGL ES Render to texture。

基本上，您必須將第一個濾鏡應用到原始圖像並將結果存儲在紋理中（而不是系統提供的幀緩衝區）。然後使用包含過濾圖像的結果紋理作爲下一個過濾器的輸入，並再次渲染紋理。重複，直到您到達鏈條的最後一個過濾器。此時，在執行渲染之前還原原始幀緩衝區對象，以便能夠在屏幕上顯示結果。

這裏是如何做到這一點的2個過濾器的一些示例代碼：

// 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, width, height, 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 
... 

// 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 
...