在前面的博客中opengl 显示BMP图像，总结了如何使用opengl显示BMP图像，如何显示BMP图像序列。

在做Object detection的一些工作中，经常会将检测到object用一个框标记出来，这次探索一下如何实现这个功能。

这要使用Opengl的blend功能。

void glBlendFunc(GLenum sfactor,GLenum dfactor);

sfactor

指定如何计算红色，绿色，蓝色和alpha源混合因子。下列符号常量被接受：GL_ZERO，GL_ONE，GL_SRC_COLOR，GL_ONE_MINUS_SRC_COLOR，GL_DST_COLOR，GL_ONE_MINUS_DST_COLOR，GL_SRC_ALPHA，GL_ONE_MINUS_SRC_ALPHA，GL_DST_ALPHA，GL_ONE_MINUS_DST_ALPHA，GL_CONSTANT_COLOR，GL_ONE_MINUS_CONSTANT_COLOR，GL_CONSTANT_ALPHA，GL_ONE_MINUS_CONSTANT_ALPHA和GL_SRC_ALPHA_SATURATE。初始值为GL_ONE。

dfactor

指定如何计算红色，绿色，蓝色和alpha目标混合因子。接受以下符号常量：GL_ZERO，GL_ONE，GL_SRC_COLOR，GL_ONE_MINUS_SRC_COLOR，GL_DST_COLOR，GL_ONE_MINUS_DST_COLOR，GL_SRC_ALPHA，GL_ONE_MINUS_SRC_ALPHA，GL_DST_ALPHA，GL_ONE_MINUS_DST_ALPHA。 GL_CONSTANT_COLOR，GL_ONE_MINUS_CONSTANT_COLOR，GL_CONSTANT_ALPHA和GL_ONE_MINUS_CONSTANT_ALPHA。初始值为GL_ZERO。

其实原理还时很简单的，图片是一个图层，将框画到另外一个图层上面，将这两个图层进行alpha blending即可。

能用代码说明的问题，尽量上代码：

// show_yuv422p.cpp : Defines the entry point for the console application.
//#include "stdafx.h"#include <GLTools.h>	// OpenGL toolkit
#include <GLShaderManager.h>#ifdef __APPLE__
#include <glut/glut.h>
#else
#define FREEGLUT_STATIC
#include <GL/glut.h>
#endif#include <GL/glew.h>
#include <GL/freeglut.h>
#include <stdio.h>
#include <stdlib.h>
#include <malloc.h>
#include <string.h>#include <Windows.h>#include <iostream>
using namespace std;// settings
const int SCR_WIDTH = 640, SCR_HEIGHT = 480;
GLuint base_prog;
GLuint quad_vbo;
GLuint tex;
unsigned char* image;GLShaderManager	shaderManager;
GLBatch	squareBatch;
GLfloat blockSize = 0.2f;
GLfloat vVerts[] = { -blockSize, -blockSize, 0.0f,
blockSize, -blockSize, 0.0f,
blockSize, blockSize, 0.0f,
-blockSize, blockSize, 0.0f };//----------------------------------------------------------------------------
void glAttachShaderSource(GLuint prog, GLenum type, const char * source)
{GLuint sh;sh = glCreateShader(type);glShaderSource(sh, 1, &source, NULL);glCompileShader(sh);char buffer[4096];glGetShaderInfoLog(sh, sizeof(buffer), NULL, buffer);glAttachShader(prog, sh);glDeleteShader(sh);
}//----------------------------------------------------------------------------
void Init()
{glClearColor(0.0, 0.0, 0.0, 0.0);glEnable(GL_DEBUG_OUTPUT);//(1) 编写Vertex shader和 Fragment Shaderstatic const char quad_shader_vs[] ="#version 330 core\n""\n""layout (location = 0) in vec2 in_position;\n""layout (location = 1) in vec2 in_tex_coord;\n""\n""out vec2 tex_coord;\n""\n""void main(void)\n""{\n""    gl_Position = vec4(in_position, 0.0, 1.0);\n""    tex_coord = in_tex_coord;\n""}\n";static const char quad_shader_fs[] ="#version 330 core\n""\n""in vec2 tex_coord;\n""\n""layout (location = 0) out vec4 color;\n""\n""uniform sampler2D tex;\n""\n""void main(void)\n""{\n""    color = texture(tex,tex_coord);\n""}\n";//(2) 创建两个Shader实例//创建Program对象base_prog = glCreateProgram();//绑定shader到program对象glAttachShaderSource(base_prog, GL_VERTEX_SHADER, quad_shader_vs);glAttachShaderSource(base_prog, GL_FRAGMENT_SHADER, quad_shader_fs);//链接programglLinkProgram(base_prog);//初始化Texture//定义定点数组static const GLfloat quad_data[] ={-1.0f, -1.0f,1.0f, -1.0f,-1.0f, 1.0f,1.0f, 1.0f,/*0.0f, 1.0f,1.0f, 1.0f,0.0f, 0.0f,1.0f, 0.0f,*/0.0f, 0.0f,1.0f, 0.0f,0.0f, 1.0f,1.0f, 1.0f,};glGenBuffers(1, &quad_vbo);glBindBuffer(GL_ARRAY_BUFFER, quad_vbo);glBufferData(GL_ARRAY_BUFFER, sizeof(quad_data), quad_data, GL_STATIC_DRAW);glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 0, (GLvoid*)0);/*glVertexAttribPointer(GLuint index, GLint size, GLenum type, GLboolean normalized, GLsizei stride, const void *ptr);函数的意义是为 Atrtribute 变量制定VBO中的数据。参数：1): index  ， Attribute的索引2): size, Attribute 变量数据是由几个元素组成的， x, y, z, w; 最多四个。3): normalized, 是否归一化， 编程1.0以内的数，这样做的目的是减少向gpu传递数据的带宽。4): stride, 元素间隔, ， 通常是0*/glEnableVertexAttribArray(0);glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 0, (const GLvoid*)(8 * sizeof(float)));glEnableVertexAttribArray(1);char buf[1024];glGetProgramInfoLog(base_prog, 1024, NULL, buf);printf("Program Info Log = %s\n", buf);glPixelStorei(GL_UNPACK_ALIGNMENT, 4);/*void glPixelStorei(GLenum pname,GLint param);它含有两个参数：pname：指定所要被设置参数的符号名。这里，参数的符号名有两种一种是GL_PACK_ALIGNMENT，它影响将像素数据写回到主存的打包形式，对glReadPixels的调用产生影响；还有一种是GL_UNPACK_ALIGNMENT，它影响从主存读到的像素数据的解包形式，对glTexImage2D以及glTexSubImage2D产生影响。param：指定相应的pname设置为什么值。这个数值一般是1、2、4或8，用于指定存储器中每个像素行有多少个字节对齐。对齐的字节数越高，系统就越能优化。在实际代码中，我们看到的是glPixelStorei(GL_UNPACK_ALIGNMENT, 1);实际上，我们可以这里可以用4（默认值）。因为checkImage能够保证是4字节对齐的。当然，我们可以通过对checkImage的修改使其保证是8字节对齐：*/// textureglGenTextures(1, &tex);glBindTexture(GL_TEXTURE_2D, tex);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_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);//如果你想加载视频帧，或图片序列，你需要将以下的glTexImage2D（）代码放到display()函数中，并且加上计时函数以便更新画面，如果从摄像机读的帧数据直接贴也是可以的int width, height;FILE *fp = fopen("D:\\vmshare\\show_yuv422p\\show_yuv422p_on_screen_00000001.bmp", "rb");if (!fp) {printf("read file error\n");return;}unsigned char buff[4] = { 0 };fseek(fp, 18, SEEK_SET);fread(buff, 1, 4, fp);width = (buff[3] << 24) + (buff[2] << 16) + (buff[1] << 8) + buff[0];memset(buff, 0, sizeof(buff));fread(buff, 1, 4, fp);height = (buff[3] << 24) + (buff[2] << 16) + (buff[1] << 8) + buff[0];int line_stride = (width * 3 + 3) / 4 * 4;image = (unsigned char *)calloc(1, height * line_stride);fseek(fp, 54, SEEK_SET);fread(image, 1, height * line_stride, fp);fclose(fp);if (image){glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_BGR, GL_UNSIGNED_BYTE, image);}else{printf("Failed to load texture");}glBindTexture(GL_TEXTURE_2D, 0);shaderManager.InitializeStockShaders();//GLint line_width = 0;//glGetIntegerv(GL_ALIASED_LINE_WIDTH_RANGE, &line_width);//printf("max line width is = %d\n", line_width);// Load up a triangle fan//squareBatch.Begin(GL_TRIANGLE_FAN, 4);//squareBatch.Begin(GL_LINE_STRIP, 4);squareBatch.Begin(GL_LINE_LOOP, 4);glLineWidth(2.0f);squareBatch.CopyVertexData3f(vVerts);squareBatch.End();}void load_frame(unsigned char *frame_rgb_buf, int *w, int *h)
{char tmp_buf[1024] = { 0 };static int index = 1;sprintf(tmp_buf, "D:\\vmshare\\show_yuv422p\\show_yuv422p_on_screen_%08d.bmp", index++);int width, height;FILE *fp = fopen(tmp_buf, "rb");if (!fp) {printf("read file error\n");return;}printf("read file %s\n", tmp_buf);unsigned char buff[4] = { 0 };fseek(fp, 18, SEEK_SET);fread(buff, 1, 4, fp);width = (buff[3] << 24) + (buff[2] << 16) + (buff[1] << 8) + buff[0];memset(buff, 0, sizeof(buff));fread(buff, 1, 4, fp);height = (buff[3] << 24) + (buff[2] << 16) + (buff[1] << 8) + buff[0];int line_stride = (width * 3 + 3) / 4 * 4;fseek(fp, 54, SEEK_SET);fread(frame_rgb_buf, 1, height * line_stride, fp);fclose(fp);*w = width;*h = height;
}
//----------------------------------------------------------------------------
void add_rect_roi()
{//glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);GLfloat vRed[] = { 1.0f, 0.0f, 0.9f, 0.5f };glEnable(GL_BLEND);glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);shaderManager.UseStockShader(GLT_SHADER_IDENTITY, vRed);squareBatch.Draw();glDisable(GL_BLEND);
}void display(void)
{int width = 0;int height = 0;load_frame(image, &width, &height);if (image){glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_BGR, GL_UNSIGNED_BYTE, image);}else{printf("Failed to load texture");}//glBindTexture(GL_TEXTURE_2D, 0);glClearColor(0.0, 255, 0.0, 0.0);glClear(GL_COLOR_BUFFER_BIT);glUseProgram(base_prog);glActiveTexture(GL_TEXTURE0);glBindTexture(GL_TEXTURE_2D, tex);glUniform1i(glGetUniformLocation(base_prog, "tex"), 0);glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);add_rect_roi();glutSwapBuffers();
}//----------------------------------------------------------------------------
void OnShutdown()
{glUseProgram(0);glDeleteProgram(base_prog);glDeleteTextures(1, &tex);glDeleteVertexArrays(1, &tex);//销毁vboglDeleteBuffers(1, &quad_vbo);printf("Shutdown successfull");if (image) {free(image);image = NULL;}
}void timeFunc(int value){display();// Present frame every 40 msglutTimerFunc(40, timeFunc, 0);
}int main(int argc, char **argv)
{glutInit(&argc, argv);glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA);glutInitWindowPosition(100, 100);glutInitWindowSize(SCR_WIDTH, SCR_HEIGHT);glutCreateWindow("GL_MultiThread_Video");printf("Version: %s\n", glGetString(GL_VERSION));if (glewInit() != GLEW_OK){printf("Failed to initialize GLEW ... exiting");exit(EXIT_FAILURE);}Init();glutDisplayFunc(display);glutTimerFunc(40, timeFunc, 0);glutCloseFunc(OnShutdown);glutMainLoop();return 0;
}

可以通过glLineWidth修改线宽。

如果将这个项目持续下去，下次可以弄一段YUV序列来播放一下。

如果在框上再画一些东西，该如何做呢？多层融合该如何实现呢？稍后分解