OpenGL入门05.纹理贴图

Posted 2022-11-28 stq_wyy

在OpenGL中，我们渲染出来的画面是一张图片，纹理贴图由像素组成，每个像素又包含4个通道的数据，即RGBA，我们能看到RGB的颜色。这篇文章将介绍如何加载图片，解码图片，并把它贴到几何形体上。

首先我们需要对原有代码封装一下，添加一个通用工具脚本Utils.h和Utils.h。后续一些通用的方法都放在这里边。

Utils.h:

#pragma once
#include <stdio.h>

unsigned char* LoadFileContent(const char* filePath);

Utils.cpp:

#include "Utils.h"

unsigned char* LoadFileContent(const char* filePath)

	unsigned char* fileContent = nullptr;

	FILE* pFile = fopen(filePath, "rb");

	if (pFile)
	
		fseek(pFile, 0, SEEK_END);
		int nLen = ftell(pFile);
		if (nLen > 0)
		
			rewind(pFile);
			fileContent = new unsigned char[nLen + 1];
			fread(fileContent, sizeof(unsigned char), nLen, pFile);
			fileContent[nLen] = '\\0';
		
		fclose(pFile);
	

	return fileContent;

LoadFileContent方法读取文件到内存中。然后我们添加texture.h和texture.cpp文件。

texture.h:

#pragma once
#include <windows.h>
#include <gl/GL.h>

class Texture

public:
	GLuint mTextureID;
	void Init(const char* imagePath);
;

texture.cpp:

#include "texture.h"
#include "Utils.h"

unsigned char* DecodeBMP(unsigned char* bmpFileData, int& width, int& height)

	if (0x4D42 == *((unsigned short*)bmpFileData))
	
		int pixelDataOffset = *((int*)(bmpFileData + 10));
		width = *((int*)(bmpFileData + 18));
		height = *((int*)(bmpFileData + 22));
		unsigned char* pixelData = bmpFileData + pixelDataOffset;

		//转码成rgb
		for (int i=0;i<width*height*3;i+=3)
		
			unsigned char temp = pixelData[i];
			pixelData[i] = pixelData[i + 2];
			pixelData[i + 2] = temp;
		

		return pixelData;
	
	else
	
		return nullptr;
	


void Texture::Init(const char* imagePath)

	//加载图片文件到内存中
	unsigned char* imageFileContent = LoadFileContent(imagePath);

	//解码
	int width = 0, height = 0;
	unsigned char* pixelData = DecodeBMP(imageFileContent, width, height);
	//生成opengl图片
	glGenTextures(1, &mTextureID);

	glBindTexture(GL_TEXTURE_2D, mTextureID);

	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);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);
	//纹理从内存传到显存
	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, pixelData);
	glBindTexture(GL_TEXTURE_2D, 0);

	delete imageFileContent;

在texture.cpp里我们把加载到内存的图片进行了转码，生成OpenGL图片，接下来我们把图片贴到场景中的物体上：

//指定纹理坐标
glTexCoord2f(0.0f, 0.0f);
glVertex3f(-1.0f, -0.5f, -2.0f);

glNormal3f(0.0f, 1.0f, 0.0f);
glTexCoord2f(1.0f, 0.0f);
glVertex3f(1.0f,-0.5f, -2.0f);
		
glNormal3f(0.0f, 1.0f, 0.0f);
glTexCoord2f(0.0f, 1.0f);
glVertex3f(-1.0f, -0.5f, -3.0f);


glNormal3f(1.0f, 0.0f, 0.0f);
glTexCoord2f(1.0f, 0.0f);
glVertex3f(1.0f, -0.5f, -2.0f);

glNormal3f(0.0f, 1.0f, 0.0f);
glTexCoord2f(1.0f, 1.0f);
glVertex3f(1.0f, -0.5f, -3.0f);

glNormal3f(0.0f, 1.0f, 0.0f);
glTexCoord2f(0.0f, 1.0f);
glVertex3f(-1.0f, -0.5f, -3.0f);

看下效果：

这个效果图受到光照影响更明显了~