//////////////////////////////////////////////////////////////////////////////////////
//移动三角形 颜色变换
//作者：青丝成霜
//////////////////////////////////////////////////////////////////////////////////////
#include <stdio.h>
#include <stdlib.h>
#include <GL/glew.h>
#include "readtext.h"

#ifdef _APPLE_
#include <glut/glut.h>
#else
#define FREEGLUT_STATIC
#include <GL/glut.h>
#endif

#pragma  comment(lib, "readtext.lib")

GLuint vShader, fShader, programHandle;

GLint  vaoHandle, vboHandles[2], positionBufferHandle, colorBufferHandle;

GLuint elapseTimeUniformLocation, loopDurationLocation, fragLoopDurationLocation;
GLint positionLocation, colorLocation;

//////////////////////////////////////////////////////////////////////////////////////////////////////////////////
//////////////////////////////////////////////////////////////////
int infoLogLength =0;
int charWritten =0;
char *infoLog;

/////////////////////////////////////////////////////////////////////////////////////////////////////////////////
//////////////////////////////////////////////////////////////////////
float positionData[]={  0.8f, 0.0f, 0.0f, 
                       -0.8f, 0.0f, 0.0f, 
					    0.0f, 0.8f, 0.0f};
//////////////////////////////////////////
//float colorData[]= { 1.0, 0.0, 0.0,
//                     0.0, 1.0, 0.0,
//					   0.0, 0.0, 1.0};
//
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
void SetupShader()
{
	char *renderer;
	char *vender;
	char *version;
	char *glslVersion;

	////////////////////////////////////
	char *vs, *fs;
	char *vv, *ff;
	char *txt;
	/////////////////////////////////////////////////////////////
	renderer =glGetString(GL_RENDERER);
	vender =glGetString(GL_VENDOR);
	version =glGetString(GL_VERSION);
	glslVersion =glGetString(GL_SHADING_LANGUAGE_VERSION);

	printf("graphic card:\t%s \n", renderer);
	printf("graphic company:\t%s \n", vender);
	printf("openGL version:\t%s \n", version);
	printf("GLSL version:\t %s \n", glslVersion);
	printf("*****************************************************\n");
	//////////////////////////////////////////////////////////////
    //txt =readText("2.txt");
	//printf("%s\n",txt);
	//putchar(10);
	vShader =glCreateShader(GL_VERTEX_SHADER);

	vs =readText("shader/triangle.vert");
	//printf("%s\n",vs);
	vv =vs;
	

	if(vShader ==0)
	{
		printf("Error: fail to create shader!");
		exit(1);
	}

	glShaderSource(vShader, 1, &vv, NULL);
	glCompileShader(vShader);
	free(vs);

	glGetShaderiv(vShader, GL_INFO_LOG_LENGTH, &infoLogLength);
	if(infoLogLength >0)
	{
		infoLog =(char *)malloc(infoLogLength);
		glGetShaderInfoLog(vShader, infoLogLength, &charWritten, infoLog);
		printf("%s\n", infoLog);
		printf("**********************************************************\n");
		free(infoLog);
	}

	/////////////////////////////////////////////////////////////////////////////////
	fShader =glCreateShader(GL_FRAGMENT_SHADER);
	if(fShader ==0)
	{
		printf("can‘t create fragment shader! \n");
		exit(1);
	}
    
	fs =readText("shader/triangle.frag");
    //printf("%s \n",fs);
	ff= fs;
	glShaderSource(fShader, 1, &ff, NULL);
	glCompileShader(fShader);
	free(fs);

	glGetShaderiv(fShader, GL_INFO_LOG_LENGTH, &infoLogLength);

	if(infoLogLength >0)
	{
		infoLog =(char *)malloc(infoLogLength);
		glGetShaderInfoLog(fShader, infoLogLength, &charWritten, infoLog);
		////////charWritten is 
		printf("%s \n",infoLog);
		printf("***********************************************************\n");
		free(infoLog);
	}
	////////////////////////////////////
	//////////////////////////////////////
	programHandle =glCreateProgram();

	glAttachShader(programHandle, vShader);
	glAttachShader(programHandle, fShader);

	glLinkProgram(programHandle);
	
	glGetProgramiv(programHandle, GL_INFO_LOG_LENGTH, &infoLogLength);
	if(infoLogLength >0)
	{
		infoLog =(char *)malloc(infoLogLength);
		glGetProgramInfoLog(programHandle, infoLogLength, &charWritten, infoLog);
		printf("%s \n", infoLog);
		printf("**************************************************************************\n");
		free(infoLog);
	}	

	glUseProgram(programHandle);
}

/////////////////////////////////////////////////////////////////////////////////////
/////////////////////////////////////////////////////////////////////////////////////

void InitVBO()
{
	glGenBuffers(2, vboHandles);
	positionBufferHandle =vboHandles[0];
	//colorBufferHandle =vboHandles[1];
    
	//////////////////////////////////////
	glBindBuffer(GL_ARRAY_BUFFER, positionBufferHandle);
	glBufferData(GL_ARRAY_BUFFER, sizeof(positionData), positionData,GL_STATIC_DRAW);

	//glBindBuffer(GL_ARRAY_BUFFER, colorBufferHandle);
	//glBufferData(GL_ARRAY_BUFFER, sizeof(colorData), colorData, GL_STATIC_DRAW);
	//////////////////////////////////////////
    glGenVertexArrays(1, &vaoHandle);
	glBindVertexArray(vaoHandle);
	/////////////////////////////////////////////
	
	glEnableVertexAttribArray(0);
	//glEnableVertexAttribArray(1);

	///////////////////////////////////
	glBindBuffer(GL_ARRAY_BUFFER, positionBufferHandle);
	glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, NULL);

	//glBindBuffer(GL_ARRAY_BUFFER, colorBufferHandle);
	//glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 0, NULL);
}

/////////////////////////////////////////////////////////////////////////////////////
//////////////////////////////////////////////////////////////////////////////////////////
void SetupRC()
{
	glewInit();

	SetupShader();

	InitVBO();

	glClearColor(1.0, 0.0, 0.0, 1.0);
}
/////////////////////////////////////////////////////////////////////
///////////////////////////////////////////////////////////////////////
void RenderScene()
{
	glClear(GL_COLOR_BUFFER_BIT );

	glBindVertexArray(vaoHandle);
	glDrawArrays(GL_TRIANGLES, 0, 3);
	glBindVertexArray(0);

	elapseTimeUniformLocation =glGetUniformLocation(programHandle, "time");
	fragLoopDurationLocation =glGetUniformLocation(programHandle,"fragLoopDuration");
    loopDurationLocation =glGetUniformLocation(programHandle, "loopDuration");
	//printf("%d\t%d\t",elapseTimeUniformLocation, loopDurationLocation);

	glUniform1f(loopDurationLocation, 5.0f);
	glUniform1f(fragLoopDurationLocation, 10.0f);
	glUniform1f(elapseTimeUniformLocation, glutGet(GLUT_ELAPSED_TIME)/1000.0f );

	glutSwapBuffers();
	glutPostRedisplay();
}

///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
int main(int argc, char *argv[])
{
	glutInit(&argc, argv);
	glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA);

	glutInitWindowSize(800, 600);
	glutInitWindowPosition(0,0);
	glutCreateWindow("second triangle:active!");

	SetupRC();
	glutDisplayFunc(RenderScene);
	
	glutMainLoop();
	return 0;
}

triangle.vert

#version 400


layout(location =0) in vec3 vertexPosition;



uniform float loopDuration;

uniform float time;



void main()

{

	float timeScale = 3.14159f * 2.0f / loopDuration;

	float currTime = mod(time, loopDuration);


	vec4 totalOffset = vec4(cos(currTime * timeScale) * 0.5f,
				
sin(currTime * timeScale) * 0.5f, 
0.0f,
0.0f);


	gl_Position = vec4(vertexPosition,1.0) + totalOffset;

}

#version 400


out vec4 fragColor;

uniform float fragLoopDuration;
uniform float time;

const vec4 firstColor =vec4(1.0f, 0.0f, 0.0f, 1.0f);
const vec4 secondColor =vec4(0.0f, 1.0f, 0.0f, 1.0f);

void main(){
	float currentTime =mod(time, fragLoopDuration);
	float currentLerp =currentTime/fragLoopDuration;


	fragColor =mix(firstColor, secondColor, currentLerp);

 }

GLSL变换颜色的三角形(C语言)