opengl 三角纹理绘制

对上一篇的改良，使用三角形来进行快速绘制

#include "stdafx.h"
#include <iostream>
#include <fstream>
#include <cassert>
#include <gl/glew.h>
#include <gl/glut.h>

#pragma comment(lib, "glew32.lib")

using namespace std;
static GLuint txtID = 0;
static GLuint vbo[3] = {0};
static int angle = 0;

//Vbo索引
static enum 
{
	Index_Vertex = 0,
	Index_Texture_Coord,
	Index_Vertex_Element_Array,
};

//修改为始终绘制三角形
void readBitmp24(const std::string& filename, void* &ptr, int &width, int &height, int& totals)
{
	fstream in(filename.c_str(), ios_base::in|ios_base::binary);
	if (!in)
	{
		ptr = NULL;
		return;
	}

	in.seekg(0x12); //18个字节开始读取宽度和高度
	in.read((char*)&width, sizeof(int));
	in.read((char*)&height,sizeof(int));

	//BMP的每行按照4个字节对齐
	int realWidth = width;
	int lineLength = width*3;
	while (lineLength % 4 != 0)
		++lineLength;

	totals = lineLength * height;
	ptr = new char[totals];

	in.seekg(0x36); //54开始是数据，按照行读取
	in.read((char*)ptr, totals);

	//将BGR模式转换为RGB模式
	char *startPos = NULL,*curPos = NULL;
	for (int i=0; i<height; ++i)
	{
		curPos = ((char*)ptr+i*lineLength);
		for (int j=0; j<realWidth;++j)
		{
			std::swap(curPos[0], curPos[2]);
			curPos += 3;
		}
	}
	
	in.close();
}

void init()
{
	glClearColor(0,0,0,0);
	glClearDepth(1.0);

	glPixelStorei(GL_UNPACK_ALIGNMENT,4);
	glEnable(GL_DEPTH_TEST);
	glEnable(GL_LINE_SMOOTH);
	glEnable(GL_POLYGON_SMOOTH);
	glBlendFunc(GL_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
	glEnable(GL_BLEND);
	
	glGenTextures(1, &txtID);
	assert(txtID);

	glBindTexture(GL_TEXTURE_2D, txtID);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_R, GL_REPEAT);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);

	//void* oldData = NULL;
	void* bmpData = NULL;
	int width=0, height=0, totals=0,depth=0;
	readBitmp24("e:/test.bmp",bmpData,width, height,totals);
	assert(bmpData);//客户端数据，暂时不释放

	glEnable(GL_TEXTURE_2D);
	glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL);
	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height,  0, GL_RGB, GL_UNSIGNED_BYTE, bmpData);
	GLenum ffff = glGetError();
	glBindTexture(GL_TEXTURE_2D, 0);

	//校验结果
	assert(glGetError() == GLEW_NO_ERROR);

	GLfloat txtCoords[][2]=
	{
		{0,0},
		{0,1},
		{1,1},
		{1,0},
	};
	GLfloat vertex[12] = {0};

	//VBO buffers
	glGenBuffers(3,vbo);

	//顶点
	glBindBuffer(GL_ARRAY_BUFFER, vbo[Index_Vertex]);
	glBufferData(GL_ARRAY_BUFFER, sizeof(GLfloat)*12, vertex, GL_STATIC_DRAW);
	glVertexPointer(3, GL_FLOAT, 0, 0);
	glEnableClientState(GL_VERTEX_ARRAY);
	glBindBuffer(GL_ARRAY_BUFFER, 0);

	//纹理坐标
	glBindBuffer(GL_ARRAY_BUFFER, vbo[Index_Texture_Coord]);
	glBufferData(GL_ARRAY_BUFFER, sizeof(txtCoords), txtCoords, GL_STATIC_DRAW);
	glTexCoordPointer(2, GL_FLOAT, 0, 0);
	glEnableClientState(GL_TEXTURE_COORD_ARRAY);
	glBindBuffer(GL_ARRAY_BUFFER, 0);

	GLenum errorInfo = glGetError();
	assert(glGetError() == GLEW_NO_ERROR);
	delete[] bmpData;
}

void reshape(int width, int height)
{
	glViewport(0, 0, width, height);
	float factor = width*1.0/height;

	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	gluPerspective(60, factor, 1, 10);
	
	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();
}

void display()
{
	glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
	glLoadIdentity();
	glTranslatef(0,0,-3);
	glRotatef(angle,1,1,0);
	glColor4f(1,1,1,0.8);
	
	//顶点
	static GLfloat vertexs[][3] = {
		{-1, -1, -1},
		{-1, 1, -1},
		{1, 1, -1},
		{1, -1, -1},
		{-1, -1, 1},
		{-1, 1, 1},
		{1, 1, 1},
		{1, -1, 1},
	};

	//面索引
	static GLubyte indices[][4] ={
		{3,2,1,0},
		{7,6,2,3},
		{4,5,6,7},
		{0,1,5,4},
		{5,1,2,6},
		{0,4,7,3},
	};

	static const int rectCnt = sizeof(indices)/4;

	glBindTexture(GL_TEXTURE_2D, txtID);
	glBindBuffer(GL_ARRAY_BUFFER, vbo[Index_Vertex]);
	GLfloat* mapBuffer = 0;
	for (int i=0; i<rectCnt; ++i)
	{
		mapBuffer = (GLfloat*)glMapBuffer(GL_ARRAY_BUFFER, GL_READ_WRITE);
		for (int j=0; j<4; ++j)
		{
			mapBuffer[j*3] = vertexs[indices[i][j]] [0];
			mapBuffer[j*3+1] = vertexs[indices[i][j]] [1];
			mapBuffer[j*3+2] = vertexs[indices[i][j]] [2];
		}
		glUnmapBuffer(GL_ARRAY_BUFFER);
		glDrawArrays(GL_TRIANGLE_FAN, 0,4);
	}
	glBindBuffer(GL_ARRAY_BUFFER, 0);

	glutSwapBuffers();
}

void idle()
{
	angle += 1;
	angle %= 360;
	glutPostRedisplay();
}

int _tmain(int argc, _TCHAR* argv[])
{
	glutInit(&argc, argv);
	glutInitDisplayMode(GLUT_DOUBLE|GLUT_RGBA|GLUT_DEPTH);
	glutInitWindowPosition(100, 100);
	glutInitWindowSize(600,600);
	glutCreateWindow("Texture2D");

	GLenum error = glewInit();
	assert(error == GLEW_NO_ERROR);
	init();
	glutDisplayFunc(display);
	glutReshapeFunc(reshape);
	glutIdleFunc(idle);
	glutMainLoop();

	return 0;
}