opengl 在显示的图像视频上画框

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 	// OpenGL toolkit
#include 

#ifdef __APPLE__
#include 
#else
#define FREEGLUT_STATIC
#include 
#endif

#include 
#include 
#include 
#include 
#include 
#include 


#include 

#include 
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 Shader
	static 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program
	glLinkProgram(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：
	*/

	// texture
	glGenTextures(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vbo
	glDeleteBuffers(1, &quad_vbo);
	printf("Shutdown successfull");

	if (image) {
		free(image);
		image = NULL;
	}
}


void timeFunc(int value){
	display();
	// Present frame every 40 ms
	glutTimerFunc(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