Skybox.cpp

#include "Skybox.h"
#include "Camera.h"

#include "mat.h"
#include "program.h"

#define STB_IMAGE_IMPLEMENTATION
#include "stb_image.h"

void Skybox::CreateCubeMap(
	const char* front,
	const char* back,
	const char* top,
	const char* bottom,
	const char* left,
	const char* right)
{
	// generate a cube-map texture to hold all the sides
	glActiveTexture(GL_TEXTURE0);
	glGenTextures(1, &texCube);

	// load each image and copy into a side of the cube-map texture
	load_cube_map_side(texCube, GL_TEXTURE_CUBE_MAP_NEGATIVE_Z, front);
	load_cube_map_side(texCube, GL_TEXTURE_CUBE_MAP_POSITIVE_Z, back);
	load_cube_map_side(texCube, GL_TEXTURE_CUBE_MAP_POSITIVE_Y, top);
	load_cube_map_side(texCube, GL_TEXTURE_CUBE_MAP_NEGATIVE_Y, bottom);
	load_cube_map_side(texCube, GL_TEXTURE_CUBE_MAP_NEGATIVE_X, left);
	load_cube_map_side(texCube, GL_TEXTURE_CUBE_MAP_POSITIVE_X, right);

	// format cube map texture
	glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MAG_FILTER, GL_LINEAR_MIPMAP_LINEAR);
	glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
	glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_R, GL_CLAMP_TO_EDGE);
	glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
	glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

	glActiveTexture(GL_TEXTURE0);
	glBindTexture(GL_TEXTURE_CUBE_MAP, texCube);
	glGenerateMipmap(GL_TEXTURE_CUBE_MAP);
	glBindTexture(GL_TEXTURE_CUBE_MAP, 0);
}

bool Skybox::load_cube_map_side(GLuint texture, GLenum side_target, const char* file_name)
{
	glBindTexture(GL_TEXTURE_CUBE_MAP, texture);

	int x, y, n;
	int force_channels = 4;
	unsigned char*  image_data = stbi_load(file_name, &x, &y, &n, force_channels);
	if (!image_data) {
		fprintf(stderr, "ERROR: could not load %s\n", file_name);
		return false;
	}
	// non-power-of-2 dimensions check
	if ((x & (x - 1)) != 0 || (y & (y - 1)) != 0) {
		fprintf(stderr,
			"WARNING: image %s is not power-of-2 dimensions\n",
			file_name);
	}

	// copy image data into 'target' side of cube map
	glTexImage2D(
		side_target,
		0,
		GL_RGBA,
		x,
		y,
		0,
		GL_RGBA,
		GL_UNSIGNED_BYTE,
		image_data);
	free(image_data);
	return true;
}