OpenGL Texture Atlas Array Texture Example

texture_atlas.cpp

// tiles_x the amount of tiles in the image in the x dimension
// tiles_y the amount of tiles in the image in the y dimension
void Texture::finalizeArray(GLsizei tiles_x, GLsizei tiles_y) {
	
	// read in file data
	Material* mat = new Material("file.bmp"); // MUST be power of 2
	mat->mips = 1; // !single image!
	
	// defines ogl parameters
	TextureData* tdata = new TextureData;
	tdata->min_filter = GL_LINEAR;
	tdata->mag_filter = GL_LINEAR;
	tdata->wrapping = GL_CLAMP_TO_EDGE;
	
	
	// create ogl texture handle
	GLuint texid = 0;
	glGenTextures(1, &texid);
	tdata->tid = texid;
	
	
	// bind ogl texture handle
	glBindTexture(GL_TEXTURE_2D_ARRAY, tdata->tid);
		
		
		// set up texture handle parameters
		glTexParameteri(GL_TEXTURE_2D_ARRAY, GL_TEXTURE_BASE_LEVEL, 0); // !single image!
		glTexParameteri(GL_TEXTURE_2D_ARRAY, GL_TEXTURE_MAX_LEVEL,  mat->mips); // !single image! mat->mips == 1
		glTexParameteri(GL_TEXTURE_2D_ARRAY, GL_TEXTURE_MAG_FILTER, tdata->min_filter); // GL_LINEAR
		glTexParameteri(GL_TEXTURE_2D_ARRAY, GL_TEXTURE_MIN_FILTER, tdata->mag_filter); // GL_LINEAR 
		glTexParameteri(GL_TEXTURE_2D_ARRAY, GL_TEXTURE_WRAP_S,     tdata->wrapping); // GL_CLAMP_TO_EDGE
		glTexParameteri(GL_TEXTURE_2D_ARRAY, GL_TEXTURE_WRAP_T,     tdata->wrapping); // GL_CLAMP_TO_EDGE
		
		
		// do some calculation
		size_t p_dx = mat->width / tiles_x; // pixels of each tile in x
		size_t p_dy = mat->height / tiles_y; // pixels of each tile in y
		size_t tiles = tiles_x * tiles_y; // number of tiles total
		
		
		// defines boundaries of a single sub image
		// target (GL_TEXTURE_2D_ARRAY)
		// !miplevels 1 single image!
		// pformat
		// tile_width
		// tile_height
		// number of tiles
		// http://docs.gl/gl4/glTexStorage3D
		glTexStorage3D(GL_TEXTURE_2D_ARRAY, 1, GL_RGB8, p_dx, p_dy, tiles); // mips, format, width/tiles_x, height/tiles_y, total_tiles
		
		
		// alignment
		// GL_UNPACK_ROW_LENGTH defines the number of pixels in a row
		// GL_UNPACK_IMAGE_HEIGHT defines the number of pixels in a column
		// http://docs.gl/gl4/glPixelStore
		glPixelStorei(GL_UNPACK_ROW_LENGTH, mat->width); // width
		glPixelStorei(GL_UNPACK_IMAGE_HEIGHT, mat->height); // height
		
		
		// fills `tiles_x * tiles_y` boundaries with sub image data
		// reads all tiles row by row as opposed to column by column i.e. 1x1 2x1 1x2 2x2
		for (GLsizei x=0; x<tiles_x; x++) {
			for (GLsizei y=0; y<tiles_y; y++) {
				
				// target (GL_TEXTURE_2D_ARRAY)
				// miplevels 0 for just single image
				// 0 (const)
				// 0 (const)
				// x * tiles_x + y
				// tile_width
				// tiles_height
				// 1 (const)
				// pformat (GL_BGR)
				// iformat (GL_UNSIGNED_BYTE)
				// pixels + (x * tile_height * width + y * tile_width) * components
				// http://docs.gl/gl4/glTexSubImage3D
				glTexSubImage3D(GL_TEXTURE_2D_ARRAY, 0, 0, 0, x * tiles_x + y, p_dx, p_dy, 1, GL_BGR, GL_UNSIGNED_BYTE, mat->pixels + (x * p_dy * mat->width + y * p_dx) * 3);
			}
		}
	
	// unbind texture handle
	glBindTexture(GL_TEXTURE_2D_ARRAY, 0);
}