【OpenGL】高级片段着色器——高斯模糊和索贝尔边缘检测

顶点着色器 convolve.vs

#version 150
precision highp float;in vec2 position;out Fragment
{vec2 tex_coord;
} fragment;void main(void)
{gl_Position = vec4(position, 0.5, 1.0);// This produces a texture coordinate that ranges from (0.0, 0.0) to (1.0, 1.0)fragment.tex_coord = position * 0.5 + vec2(0.5, 0.5);
}

高斯模糊着色器 convolve.fs

#version 150
precision highp float;// Input interface block from vertex shader
in Fragment
{vec2 tex_coord;
} fragment;//
uniform sampler2D tex_input_image;uniform samplerBuffer tbo_coefficient;uniform vec2 tc_scale;uniform int kernel_size;out vec4 output_color;void main(void)
{int filter_size = kernel_size; // textureSize(tbo_coefficient);vec4 color = vec4(0.0);vec2 tc_offset;float coefficient;for (int i = 0; i < filter_size; i++) {coefficient = texelFetch(tbo_coefficient, i).r;tc_offset = float(i - filter_size / 2) * tc_scale;color += coefficient * texture(tex_input_image, fragment.tex_coord + tc_offset);}// output_color = texture(tex_input_image, fragment.tex_coord) * texelFetch(tbo_coefficient, 3).r;output_color = color;
}

索贝尔边缘检测片段着色器 absvalue.fs

#version 150
precision highp float;// Input interface block from vertex shader
in Fragment
{vec2 tex_coord;
} fragment;//
uniform sampler2D tex_input_image;out vec4 output_color;void main(void)
{output_color = abs(texture(tex_input_image, fragment.tex_coord));
}

#include "explode.h"ConvolutionApp::ConvolutionApp(void): screenWidth(1024 + 16), screenHeight(768 + 32)
{}void ConvolutionApp::Initialize(void)
{GLenum err = glewInit();if (GLEW_OK != err){/* Problem: glewInit failed, something is seriously wrong. */fprintf(stderr, "Error: %s\n", glewGetErrorString(err));}instancingProg = gltLoadShaderPair("convolve.vs", "convolve.fs");glBindAttribLocation(instancingProg, 0, "position");glLinkProgram(instancingProg);absValueProg = gltLoadShaderPair("convolve.vs", "absvalue.fs");glBindAttribLocation(instancingProg, 0, "position");glLinkProgram(instancingProg);glUseProgram(instancingProg);GLbyte *pBits;int nWidth, nHeight, nComponents;GLenum eFormat;// Read the texture bitspBits = gltReadTGABits("image.tga", &nWidth, &nHeight, &nComponents, &eFormat);glGenTextures(1, &sourceTexture);glBindTexture(GL_TEXTURE_2D, sourceTexture);glTexImage2D(GL_TEXTURE_2D, 0, nComponents, nWidth, nHeight, 0, eFormat, GL_UNSIGNED_BYTE, pBits);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_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);glGenFramebuffers(1, &intermediateFBO);glBindFramebuffer(GL_FRAMEBUFFER, intermediateFBO);glGenTextures(1, &intermediateTexture);glBindTexture(GL_TEXTURE_2D, intermediateTexture);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_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);glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA16F, 1027, 768, 0, GL_RGBA, GL_FLOAT, NULL);glBindTexture(GL_TEXTURE_2D, 0);glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, intermediateTexture, 0);glGenFramebuffers(1, &targetFBO);glBindFramebuffer(GL_FRAMEBUFFER, targetFBO);glGenTextures(1, &targetTexture);glBindTexture(GL_TEXTURE_2D, targetTexture);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_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);glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA16F, 1027, 768, 0, GL_RGBA, GL_FLOAT, NULL);glBindTexture(GL_TEXTURE_2D, 0);glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, targetTexture, 0);/*static const GLfloat kernel[] ={0.015625, 0.09375, 0.234375, 0.3125, 0.234375, 0.09375, 0.015625};*/static const GLfloat gaussian_kernel[] ={0.004f,0.008f,0.014f,0.022f,0.033f,0.046f,0.061f,0.076f,0.089f,0.098f,0.101f,0.098f,0.089f,0.076f,0.061f,0.046f,0.033f,0.022f,0.014f,0.008f,0.004f};/*static const GLfloat gaussian_kernel[] ={0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,1.0f,0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,0.0f};*/// glUniform2f(glGetUniformLocation(instancingProg, "tc_scale"), 1.0f / (float)nWidth, 0.0f); // 1.0f / (float)nHeight);// glUniform2f(glGetUniformLocation(instancingProg, "tc_scale"), 0.0f, 1.0f / (float)nHeight);kernelScale[0] = 1.0f / (float)nWidth;kernelScale[1] = 1.0f / (float)nHeight;glUniform1i(glGetUniformLocation(instancingProg, "tex_input_image"), 0);glUniform1i(glGetUniformLocation(instancingProg, "tbo_coefficient"), 1);glActiveTexture(GL_TEXTURE1);glGenTextures(1, &gaussian_kernelTexture);glBindTexture(GL_TEXTURE_BUFFER, gaussian_kernelTexture);glGenBuffers(1, &gaussian_kernelBuffer);glBindBuffer(GL_TEXTURE_BUFFER, gaussian_kernelBuffer);glBufferData(GL_TEXTURE_BUFFER, sizeof(gaussian_kernel), gaussian_kernel, GL_STATIC_DRAW);glTexBufferARB(GL_TEXTURE_BUFFER, GL_R32F, gaussian_kernelBuffer);static const GLfloat sobel_kernel1[] ={1.0f, 2.0, 1.0f};static const GLfloat sobel_kernel2[] ={1.0f, 0.0f, -1.0f};glGenTextures(1, &sobel_kernelTexture1);glBindTexture(GL_TEXTURE_BUFFER, sobel_kernelTexture1);glGenBuffers(1, &sobel_kernelBuffer1);glBindBuffer(GL_TEXTURE_BUFFER, sobel_kernelBuffer1);glBufferData(GL_TEXTURE_BUFFER, sizeof(sobel_kernel1), sobel_kernel1, GL_STATIC_DRAW);glTexBufferARB(GL_TEXTURE_BUFFER, GL_R32F, sobel_kernelBuffer1);glGenTextures(1, &sobel_kernelTexture2);glBindTexture(GL_TEXTURE_BUFFER, sobel_kernelTexture2);glGenBuffers(1, &sobel_kernelBuffer2);glBindBuffer(GL_TEXTURE_BUFFER, sobel_kernelBuffer2);glBufferData(GL_TEXTURE_BUFFER, sizeof(sobel_kernel2), sobel_kernel2, GL_STATIC_DRAW);glTexBufferARB(GL_TEXTURE_BUFFER, GL_R32F, sobel_kernelBuffer2);static const GLfloat square_vertices[] ={-1.0f, -1.0f,1.0f, -1.0f,-1.0f,  1.0f,1.0f,  1.0f};GLuint offset = 0;glGenVertexArrays(1, &square_vao);glGenBuffers(1, &square_vbo);glBindVertexArray(square_vao);glBindBuffer(GL_ARRAY_BUFFER, square_vbo);glBufferData(GL_ARRAY_BUFFER, sizeof(square_vertices), square_vertices, GL_STATIC_DRAW);glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 0, 0);glEnableVertexAttribArray(0);
}void ConvolutionApp::Shutdown(void)
{glDeleteBuffers(1, &square_vbo);glDeleteVertexArrays(1, &square_vao);
}void ConvolutionApp::Resize(GLsizei nWidth, GLsizei nHeight)
{screenWidth = nWidth;screenHeight = nHeight;glViewport(0, 0, nWidth, nHeight);
}void ConvolutionApp::Render(void)
{glUseProgram(instancingProg);glBindVertexArray(square_vao);//高斯模糊glActiveTexture(GL_TEXTURE1);glBindTexture(GL_TEXTURE_BUFFER, gaussian_kernelTexture);glActiveTexture(GL_TEXTURE0);glBindTexture(GL_TEXTURE_2D, sourceTexture);glBindFramebuffer(GL_FRAMEBUFFER, intermediateFBO);glClearColor(0.0f, 0.0f, 0.0f, 0.0f);glClear(GL_COLOR_BUFFER_BIT);glUniform1i(glGetUniformLocation(instancingProg, "kernel_size"), 21);glUniform2f(glGetUniformLocation(instancingProg, "tc_scale"), 0.0f, kernelScale[1]);glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);glBindFramebuffer(GL_FRAMEBUFFER, 0);glBindTexture(GL_TEXTURE_2D, intermediateTexture);glUniform2f(glGetUniformLocation(instancingProg, "tc_scale"), kernelScale[0], 0.0f);glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);/* 索贝边缘检测 代码段 开启它时需注释上面的glActiveTexture(GL_TEXTURE1);glBindTexture(GL_TEXTURE_BUFFER, sobel_kernelTexture1);glActiveTexture(GL_TEXTURE0);glBindTexture(GL_TEXTURE_2D, sourceTexture);glBindFramebuffer(GL_FRAMEBUFFER, intermediateFBO);glClearColor(0.0f, 0.0f, 0.0f, 0.0f);glClear(GL_COLOR_BUFFER_BIT);glUniform1i(glGetUniformLocation(instancingProg, "kernel_size"), 3);glUniform2f(glGetUniformLocation(instancingProg, "tc_scale"), 0.0f, kernelScale[1]);glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);glBindFramebuffer(GL_FRAMEBUFFER, targetFBO);glBindTexture(GL_TEXTURE_2D, intermediateTexture);glActiveTexture(GL_TEXTURE1);glBindTexture(GL_TEXTURE_BUFFER, sobel_kernelTexture2);glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);glBindFramebuffer(GL_FRAMEBUFFER, 0);glActiveTexture(GL_TEXTURE0);glBindTexture(GL_TEXTURE_2D, targetTexture);glUseProgram(absValueProg);glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);*/GLenum e = glGetError();
}

高斯模糊相关说明：其中sourceImage是原图纹理，作为第一个纹理目标传入，第二个纹理目标是以纹理缓冲区形式传入convolve.fs即tbo_coefficient变量，它是高斯模糊一维纹理数据，关于纹理缓冲区数据是samplerBuffer类型的，它的获取是直接根据整数纹理来拿到对应的数据，最终我们在convolve.fs得到一个经过高斯模糊的颜色值进行输出。

索贝尔边缘检测相关说明：它总共经过3次glDrawArrays进行渲染屏幕四边形。

第一次是使用sourceTexture纹理作为第一纹理和sobel_kernelTexture1作为第二纹理，去使用instancingProg着色器生成intermediateFBO捆绑的intermediateTexture；

第二次使用intermediateTexture作为第一纹理和sobel_kernelTexture2作为第二纹理，使用instancingProg着色器生成targetFBO捆绑的targetTexture；

第三次使用targetTexture纹理作为第一纹理，使用absValueProg着色器渲染，将结果输出到帧缓冲区（屏幕上）

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【OpenGL】高级片段着色器——高斯模糊和索贝尔边缘检测

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