gamecodebook/Chapter14/Texture.cpp

// ----------------------------------------------------------------
// From Game Programming in C++ by Sanjay Madhav
// Copyright (C) 2017 Sanjay Madhav. All rights reserved.
// 
// Released under the BSD License
// See LICENSE in root directory for full details.
// ----------------------------------------------------------------

#include "Texture.h"
#include <SOIL/SOIL.h>
#include <GL/glew.h>
#include <SDL/SDL.h>

Texture::Texture()
:mTextureID(0)
,mWidth(0)
,mHeight(0)
{
	
}

Texture::~Texture()
{
	
}

bool Texture::Load(const std::string& fileName)
{
	mFileName = fileName;
	int channels = 0;
	
	unsigned char* image = SOIL_load_image(fileName.c_str(),
										   &mWidth, &mHeight, &channels, SOIL_LOAD_AUTO);
	
	if (image == nullptr)
	{
		SDL_Log("SOIL failed to load image %s: %s", fileName.c_str(), SOIL_last_result());
		return false;
	}
	
	int format = GL_RGB;
	if (channels == 4)
	{
		format = GL_RGBA;
	}
	
	glGenTextures(1, &mTextureID);
	glBindTexture(GL_TEXTURE_2D, mTextureID);
	
	glTexImage2D(GL_TEXTURE_2D, 0, format, mWidth, mHeight, 0, format,
				 GL_UNSIGNED_BYTE, image);
	
	SOIL_free_image_data(image);
	
	// Generate mipmaps for texture
	glGenerateMipmap(GL_TEXTURE_2D);
	// Enable linear filtering
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

	// Enable anisotropic filtering, if supported
	if (GLEW_EXT_texture_filter_anisotropic)
	{
		// Get the maximum anisotropy value
		GLfloat largest;
		glGetFloatv(GL_MAX_TEXTURE_MAX_ANISOTROPY_EXT, &largest);
		// Enable it
		glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAX_ANISOTROPY_EXT, largest);
	}
	
	return true;
}

void Texture::Unload()
{
	glDeleteTextures(1, &mTextureID);
}

void Texture::CreateFromSurface(SDL_Surface* surface)
{
	mWidth = surface->w;
	mHeight = surface->h;
	
	// Generate a GL texture
	glGenTextures(1, &mTextureID);
	glBindTexture(GL_TEXTURE_2D, mTextureID);
	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, mWidth, mHeight, 0, GL_BGRA,
				 GL_UNSIGNED_BYTE, surface->pixels);
	
	// Use linear filtering
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
}

void Texture::CreateForRendering(int width, int height, unsigned int format)
{
	mWidth = width;
	mHeight = height;
	// Create the texture id
	glGenTextures(1, &mTextureID);
	glBindTexture(GL_TEXTURE_2D, mTextureID);
	// Set the image width/height with null initial data
	glTexImage2D(GL_TEXTURE_2D, 0, format, mWidth, mHeight, 0, GL_RGB,
		GL_FLOAT, nullptr);

	// For a texture we'll render to, just use nearest neighbor
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
}

void Texture::SetActive(int index)
{
	glActiveTexture(GL_TEXTURE0 + index);
	glBindTexture(GL_TEXTURE_2D, mTextureID);
}