OpenGL学习三十五：加载压缩TGA-白红宇

OpenGL学习三十五：加载压缩TGA

阅读量：4213 次

发布时间：2019-05-26

本文共 12636 字，大约阅读时间需要 42 分钟。

(此节内容对应NEHE教程第33课)

利用压缩算法可以减低图片大小。降低图片存储所需的物理存储空间，但是也会相应的增加图片解压缩带来的时间消耗

对于TGA文件的压缩可以简单理解为，在图片信息存储区。并不是把每一个像素点的RGB值都进行存储，而是临近的像素点如果RGB值相同，那么进行合并形成“块”对于一个”块“来说他们有一个共同的RGB值，但是块是由很多个像素点组成的

0~~11	头信息	第3位（2）是2 代表未压缩第3位（2）是10 代表未压缩RLE压缩
12~13	图像宽度	byte[13]*256+byte[12]
14~15	图像高度	byte[15]*256+byte[14]
16	图像每像素存储占用位（bit）数	24或32

接下来读一个字符代表接下来的”块“中包含的像素点数用chumk代替

如果 0<=chumk<=127 代表接下来的 chumk+1个像素点的RGB值都不同，因此每一个都需要读取

如果 128<=chumk 代表接下来的 chumk-127个像素点的RGB值相同，因此只需要读取一次即可

Texture.h

#ifndef __TEXTURE_H__#define __TEXTURE_H__#pragma comment(lib, "Opengl32.lib")					#include 
   
    																typedef	struct									{	GLubyte	* imageData;									GLuint	bpp;											GLuint	width;											GLuint	height;											GLuint	texID;											GLuint	type;				} Texture;	#endif

Tga.h

#ifndef __TGA_H__#define __TGA_H__#pragma comment(lib, "Opengl32.lib")				#include 
   
    							#include "texture.h"typedef struct{	GLubyte Header[12];									} TGAHeader;typedef struct{	GLubyte		header[6];								GLuint		bytesPerPixel;								GLuint		imageSize;								GLuint		temp;									GLuint		type;		GLuint		Height;										GLuint		Width;										GLuint		Bpp;									} TGA;TGAHeader tgaheader;								TGA tga;												GLubyte uTGAcompare[12] = {0,0,2, 0,0,0,0,0,0,0,0,0};	GLubyte cTGAcompare[12] = {0,0,10,0,0,0,0,0,0,0,0,0};	bool LoadUncompressedTGA(Texture *, char *, FILE *);	bool LoadCompressedTGA(Texture *, char *, FILE *);		#endif

TGALoader.cpp

#include "tga.h"bool LoadTGA(Texture * texture, char * filename)				{	FILE * fTGA;										fTGA = fopen(filename, "rb");									if(fTGA == NULL)											{		MessageBox(NULL, "Could not open texture file", "ERROR", MB_OK);			return false;														}	if(fread(&tgaheader, sizeof(TGAHeader), 1, fTGA) == 0)						{		MessageBox(NULL, "Could not read file header", "ERROR", MB_OK);		e		if(fTGA != NULL)															{			fclose(fTGA);															}		return false;															}	if(memcmp(uTGAcompare, &tgaheader, sizeof(tgaheader)) == 0)					{																				LoadUncompressedTGA(texture, filename, fTGA);						}	else if(memcmp(cTGAcompare, &tgaheader, sizeof(tgaheader)) == 0)			{																				LoadCompressedTGA(texture, filename, fTGA);							}	else																	{		MessageBox(NULL, "TGA file be type 2 or type 10 ", "Invalid Image", MB_OK);			fclose(fTGA);		return false;																}	return true;														}bool LoadUncompressedTGA(Texture * texture, char * filename, FILE * fTGA)	{																			if(fread(tga.header, sizeof(tga.header), 1, fTGA) == 0)						{												MessageBox(NULL, "Could not read info header", "ERROR", MB_OK);				if(fTGA != NULL)															{			fclose(fTGA);														}		return false;															}		texture->width  = tga.header[1] * 256 + tga.header[0];					texture->height = tga.header[3] * 256 + tga.header[2];						texture->bpp	= tga.header[4];										tga.Width		= texture->width;																tga.Height		= texture->height;										tga.Bpp			= texture->bpp;												if((texture->width <= 0) || (texture->height <= 0) || ((texture->bpp != 24) && (texture->bpp !=32)))		{		MessageBox(NULL, "Invalid texture information", "ERROR", MB_OK);			if(fTGA != NULL)															{			fclose(fTGA);															}		return false;															}	if(texture->bpp == 24)															texture->type	= GL_RGB;												else																			texture->type	= GL_RGBA;											tga.bytesPerPixel	= (tga.Bpp / 8);									tga.imageSize		= (tga.bytesPerPixel * tga.Width * tga.Height);			texture->imageData	= (GLubyte *)malloc(tga.imageSize);						if(texture->imageData == NULL)												{		MessageBox(NULL, "Could not allocate memory for image", "ERROR", MB_OK);			fclose(fTGA);																return false;														}	if(fread(texture->imageData, 1, tga.imageSize, fTGA) != tga.imageSize)	{		MessageBox(NULL, "Could not read image data", "ERROR", MB_OK);				if(texture->imageData != NULL)												{			free(texture->imageData);											}		fclose(fTGA);																return false;															}	// Byte Swapping Optimized By Steve Thomas	for(GLuint cswap = 0; cswap < (int)tga.imageSize; cswap += tga.bytesPerPixel)	{		texture->imageData[cswap] ^= texture->imageData[cswap+2] ^=		texture->imageData[cswap] ^= texture->imageData[cswap+2];	}	fclose(fTGA);																return true;															}bool LoadCompressedTGA(Texture * texture, char * filename, FILE * fTGA)		{ 	if(fread(tga.header, sizeof(tga.header), 1, fTGA) == 0)					{		MessageBox(NULL, "Could not read info header", "ERROR", MB_OK);				if(fTGA != NULL)															{			fclose(fTGA);														}		return false;															}	texture->width  = tga.header[1] * 256 + tga.header[0];						texture->height = tga.header[3] * 256 + tga.header[2];						texture->bpp	= tga.header[4];											tga.Width		= texture->width;											tga.Height		= texture->height;											tga.Bpp			= texture->bpp;												if((texture->width <= 0) || (texture->height <= 0) || ((texture->bpp != 24) && (texture->bpp !=32)))		{		MessageBox(NULL, "Invalid texture information", "ERROR", MB_OK);			if(fTGA != NULL)														{			fclose(fTGA);														}		return false;															}	if(texture->bpp == 24)															texture->type	= GL_RGB;												else																			texture->type	= GL_RGBA;											tga.bytesPerPixel	= (tga.Bpp / 8);										tga.imageSize		= (tga.bytesPerPixel * tga.Width * tga.Height);			texture->imageData	= (GLubyte *)malloc(tga.imageSize);					if(texture->imageData == NULL)													MessageBox(NULL, "Could not allocate memory for image", "ERROR", MB_OK);			fclose(fTGA);																return false;															}	GLuint pixelcount	= tga.Height * tga.Width;								GLuint currentpixel	= 0;												GLuint currentbyte	= 0;													GLubyte * colorbuffer = (GLubyte *)malloc(tga.bytesPerPixel);			do	{		GLubyte chunkheader = 0;													if(fread(&chunkheader, sizeof(GLubyte), 1, fTGA) == 0)						{			MessageBox(NULL, "Could not read RLE header", "ERROR", MB_OK);				if(fTGA != NULL)															{				fclose(fTGA);														}			if(texture->imageData != NULL)											{				free(texture->imageData);											}			return false;															}		if(chunkheader < 128)														{																				chunkheader++;															for(short counter = 0; counter < chunkheader; counter++)					{				if(fread(colorbuffer, 1, tga.bytesPerPixel, fTGA) != tga.bytesPerPixel) 				{					MessageBox(NULL, "Could not read image data", "ERROR", MB_OK);							if(fTGA != NULL)																		{						fclose(fTGA);																		}					if(colorbuffer != NULL)																	{						free(colorbuffer);																	}					if(texture->imageData != NULL)															{						free(texture->imageData);															}					return false;																		}																										texture->imageData[currentbyte		] = colorbuffer[2];				   				texture->imageData[currentbyte + 1	] = colorbuffer[1];				texture->imageData[currentbyte + 2	] = colorbuffer[0];				if(tga.bytesPerPixel == 4)																{					texture->imageData[currentbyte + 3] = colorbuffer[3];								}				currentbyte += tga.bytesPerPixel;														currentpixel++;																			if(currentpixel > pixelcount)															{					MessageBox(NULL, "Too many pixels read", "ERROR", NULL);								if(fTGA != NULL)																		{						fclose(fTGA);																	}						if(colorbuffer != NULL)																	{						free(colorbuffer);																	}					if(texture->imageData != NULL)															{						free(texture->imageData);															}					return false;																		}			}		}		else																					{			chunkheader -= 127;																		if(fread(colorbuffer, 1, tga.bytesPerPixel, fTGA) != tga.bytesPerPixel)					{					MessageBox(NULL, "Could not read from file", "ERROR", MB_OK);							if(fTGA != NULL)																		{					fclose(fTGA);																		}				if(colorbuffer != NULL)																	{					free(colorbuffer);																}				if(texture->imageData != NULL)															{					free(texture->imageData);														}				return false;																		}			for(short counter = 0; counter < chunkheader; counter++)								{																							texture->imageData[currentbyte		] = colorbuffer[2];								texture->imageData[currentbyte + 1	] = colorbuffer[1];				texture->imageData[currentbyte + 2	] = colorbuffer[0];				if(tga.bytesPerPixel == 4)																{					texture->imageData[currentbyte + 3] = colorbuffer[3];								}				currentbyte += tga.bytesPerPixel;														currentpixel++;																			if(currentpixel > pixelcount)															{					MessageBox(NULL, "Too many pixels read", "ERROR", NULL);								if(fTGA != NULL)																		{						fclose(fTGA);																		}						if(colorbuffer != NULL)																	{						free(colorbuffer);																	}					if(texture->imageData != NULL)															{						free(texture->imageData);														}					return false;																		}			}		}	}	while(currentpixel < pixelcount);														fclose(fTGA);																			return true;																		}

main.cpp

#include "header.h"											#include "texture.h"											bool LoadTGA(Texture *, char *);								float	spin;													Texture texture[2];												LRESULT	CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);			int LoadGLTextures()											{	int Status=FALSE;												// Load The Bitmap, Check For Errors.	if (LoadTGA(&texture[0], "Data/Uncompressed.tga") &&		LoadTGA(&texture[1], "Data/Compressed.tga"))	{		Status=TRUE;													for (int loop=0; loop<2; loop++)								{						glGenTextures(1, &texture[loop].texID);							glBindTexture(GL_TEXTURE_2D, texture[loop].texID);			glTexImage2D(GL_TEXTURE_2D, 0, texture[loop].bpp / 8, texture[loop].width, texture[loop].height, 0, texture[loop].type, GL_UNSIGNED_BYTE, texture[loop].imageData);			glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR);			glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);			if (texture[loop].imageData)									{				free(texture[loop].imageData);								}		}	}	return Status;											}void ReSizeGLScene(GLsizei width, GLsizei height)				{	if (height==0)													{		height=1;											}	glViewport(0,0,width,height);								glMatrixMode(GL_PROJECTION);								glLoadIdentity();											// Calculate The Aspect Ratio Of The Window	gluPerspective(45.0f,(GLfloat)width/(GLfloat)height,0.1f,100.0f);	glMatrixMode(GL_MODELVIEW);										glLoadIdentity();										}int InitGL(void)												{	if (!LoadGLTextures())										{		return FALSE;												}	glEnable(GL_TEXTURE_2D);										glShadeModel(GL_SMOOTH);									glClearColor(0.0f, 0.0f, 0.0f, 0.5f);							glClearDepth(1.0f);												glEnable(GL_DEPTH_TEST);										glDepthFunc(GL_LEQUAL);										glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);				return TRUE;											}void DrawGLScene(void)											{	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);			glLoadIdentity();												glTranslatef(0.0f,0.0f,-10.0f);									spin+=0.05f;													for (int loop=0; loop<20; loop++)							{		glPushMatrix();													glRotatef(spin+loop*18.0f,1.0f,0.0f,0.0f);					glTranslatef(-2.0f,2.0f,0.0f);									glBindTexture(GL_TEXTURE_2D, texture[0].texID);					glBegin(GL_QUADS);												glTexCoord2f(0.0f, 1.0f); glVertex3f(-1.0f,  1.0f, 0.0f);			glTexCoord2f(1.0f, 1.0f); glVertex3f( 1.0f,  1.0f, 0.0f);			glTexCoord2f(1.0f, 0.0f); glVertex3f( 1.0f, -1.0f, 0.0f);			glTexCoord2f(0.0f, 0.0f); glVertex3f(-1.0f, -1.0f, 0.0f);		glEnd();														glPopMatrix();													glPushMatrix();												glTranslatef(2.0f,0.0f,0.0f);									glRotatef(spin+loop*36.0f,0.0f,1.0f,0.0f);						glTranslatef(1.0f,0.0f,0.0f);									glBindTexture(GL_TEXTURE_2D, texture[1].texID);					glBegin(GL_QUADS);													glTexCoord2f(0.0f, 0.0f); glVertex3f(-1.0f,  1.0f, 0.0f);			glTexCoord2f(1.0f, 0.0f); glVertex3f( 1.0f,  1.0f, 0.0f);			glTexCoord2f(1.0f, 1.0f); glVertex3f( 1.0f, -1.0f, 0.0f);			glTexCoord2f(0.0f, 1.0f); glVertex3f(-1.0f, -1.0f, 0.0f);		glEnd();														glPopMatrix();												}	glFlush();											}void rotate(){	spin+=0.05f;	glutPostRedisplay();}void keyboard(unsigned char key,int x,int y){	switch (key)	{	case 'S':		glutIdleFunc(rotate);		break;	case 'R':		glutIdleFunc(NULL);		break;	}}int main(int argc,char **argv){	glutInit(&argc,argv);	glutInitDisplayMode(GLUT_SINGLE|GLUT_RGB|GLUT_DEPTH);	glutInitWindowSize(800,600);	glutInitWindowPosition(100,100);	glutCreateWindow("加载压缩TGA");	InitGL();	glutDisplayFunc(DrawGLScene);	glutKeyboardFunc(keyboard);	glutReshapeFunc(ReSizeGLScene);	glutMainLoop();}

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