# Texture with its own pixel data
class RootTexture
	super Texture

	redef fun root do return self

	# Has this texture been loaded yet?
	var loaded = false

	redef var gl_texture = -1

	init do all_root_textures.add self

	# Should the pixels RGB values be premultiplied by their alpha value at loading?
	#
	# All gamnit textures must have premultiplied alpha, it provides a better
	# alpha blending, avoids artifacts and allows for additive blending.
	#
	# When at `true`, the default, pixels RGB values are premultiplied
	# at loading. Set to `false` if pixels RGB values are already
	# premultiplied in the source data.
	#
	# This value must be set before calling `load`.
	var premultiply_alpha = true is writable

	private fun load_from_pixels(pixels: Pointer, width, height: Int, format: GLPixelFormat)
	do
		var max_texture_size = glGetIntegerv(gl_MAX_TEXTURE_SIZE, 0)
		if width > max_texture_size then
			error = new Error("Texture width larger than gl_MAX_TEXTURE_SIZE ({max_texture_size}) in {self} at {width}")
			return
		else if height > max_texture_size then
			error = new Error("Texture height larger than gl_MAX_TEXTURE_SIZE ({max_texture_size}) in {self} at {height}")
			return
		end

		# Premultiply alpha?
		if premultiply_alpha and format == gl_RGBA then
			pixels.premultiply_alpha(width, height)
		end

		glPixelStorei(gl_UNPACK_ALIGNEMENT, 1)
		var tex = glGenTextures(1)[0]
		gl_texture = tex

		glBindTexture(gl_TEXTURE_2D, tex)
		glTexImage2D(gl_TEXTURE_2D, 0, format, width, height, 0, format, gl_UNSIGNED_BYTE, pixels)

		glHint(gl_GENERATE_MIPMAP_HINT, gl_NICEST)
		glGenerateMipmap(gl_TEXTURE_2D)
		glTexParameteri(gl_TEXTURE_2D, gl_TEXTURE_MIN_FILTER, gl_LINEAR_MIPMAP_LINEAR)

		glBindTexture(gl_TEXTURE_2D, 0)
	end

	private fun load_checker(size: Int)
	do
		var cpixels = new CByteArray(3*size*size)

		var i = 0
		for x in [0..size[ do
			var quadrant_x = if x < size/2 then 0 else 1
			for y in [0..size[ do
				var quadrant_y = if y < size/2 then 0 else 1
				var color = if quadrant_x == quadrant_y then
					[0u8, 0u8, 0u8, 255u8]
				else [255u8, 255u8, 255u8, 255u8]

				for j in [0..3[ do cpixels[i+j] = color[j]
				i += 3
			end
		end

		width = size.to_f
		height = size.to_f
		load_from_pixels(cpixels.native_array, size, size, gl_RGB)

		cpixels.destroy
	end

	# Has this resource been deleted?
	var deleted = false

	# Delete this texture and free all its resources
	#
	# Use caution with this service as the subtextures may rely on the deleted data.
	fun delete
	do
		if deleted or not loaded then return

		deleted = true
	end
end