# Handles to reused GL buffers and texture
private class ShadowContext

	# Real screen framebuffer
	var screen_framebuffer: Int = -1

	# Framebuffer for the light point of view
	var light_view_framebuffer: Int = -1

	# Depth attached to `light_view_framebuffer`
	var depth_texture: Int = -1

	# Buffer name for vertex data
	var buffer_array: Int = -1

	# Prepare all attributes once per resolution change
	fun prepare_once(display: GamnitDisplay, shadow_resolution: Int)
	do
		assert display.gl_extensions.has("GL_OES_depth_texture")

		# Set aside the real screen framebuffer name
		var screen_framebuffer = glGetIntegerv(gl_FRAMEBUFFER_BINDING, 0)
		self.screen_framebuffer = screen_framebuffer

		# Framebuffer
		var framebuffer = glGenFramebuffers(1).first
		glBindFramebuffer(gl_FRAMEBUFFER, framebuffer)
		assert glIsFramebuffer(framebuffer)
		self.light_view_framebuffer = framebuffer
		var gl_error = glGetError
		assert gl_error == gl_NO_ERROR else print_error gl_error

		# Depth & texture/color
		var textures = glGenTextures(1)
		self.depth_texture = textures[0]
		gl_error = glGetError
		assert gl_error == gl_NO_ERROR else print_error gl_error

		resize(display, shadow_resolution)

		# Array buffer
		buffer_array = glGenBuffers(1).first
		glBindBuffer(gl_ARRAY_BUFFER, buffer_array)
		assert glIsBuffer(buffer_array)
		gl_error = glGetError
		assert gl_error == gl_NO_ERROR else print_error gl_error

		## coord
		var data = new Array[Float]
		data.add_all([-1.0, -1.0, 0.0,
	                   1.0, -1.0, 0.0,
	                  -1.0,  1.0, 0.0,
	                   1.0,  1.0, 0.0])
		## tex_coord
		data.add_all([0.0, 0.0,
		              1.0, 0.0,
		              0.0, 1.0,
		              1.0, 1.0])
		var c_data = new GLfloatArray.from(data)
		glBufferData(gl_ARRAY_BUFFER, data.length*4, c_data.native_array, gl_STATIC_DRAW)

		glBindBuffer(gl_ARRAY_BUFFER, 0)

		gl_error = glGetError
		assert gl_error == gl_NO_ERROR else print_error gl_error
	end

	# Init size or resize `depth_texture`
	fun resize(display: GamnitDisplay, shadow_resolution: Int)
	do
		glBindFramebuffer(gl_FRAMEBUFFER, light_view_framebuffer)
		var gl_error = glGetError
		assert gl_error == gl_NO_ERROR else print_error gl_error

		# Depth texture
		var depth_texture = self.depth_texture
		glActiveTexture gl_TEXTURE0
		glBindTexture(gl_TEXTURE_2D, depth_texture)
		glTexParameteri(gl_TEXTURE_2D, gl_TEXTURE_MIN_FILTER, gl_LINEAR)
		glTexParameteri(gl_TEXTURE_2D, gl_TEXTURE_MAG_FILTER, gl_NEAREST)
		glTexParameteri(gl_TEXTURE_2D, gl_TEXTURE_WRAP_S, gl_CLAMP_TO_EDGE)
		glTexParameteri(gl_TEXTURE_2D, gl_TEXTURE_WRAP_T, gl_CLAMP_TO_EDGE)
		gl_error = glGetError
		assert gl_error == gl_NO_ERROR else print_error gl_error

		# TODO support hardware shadows with GL ES 3.0 or GL_EXT_shadow_samplers
		#glTexParameteri(gl_TEXTURE_2D, gl_TEXTURE_COMPARE_MODE, ...)

		glTexImage2D(gl_TEXTURE_2D, 0, gl_DEPTH_COMPONENT,
		             shadow_resolution, shadow_resolution,
		             0, gl_DEPTH_COMPONENT, gl_UNSIGNED_SHORT, new Pointer.nul)
		gl_error = glGetError
		assert gl_error == gl_NO_ERROR else print_error gl_error

		glFramebufferTexture2D(gl_FRAMEBUFFER, gl_DEPTH_ATTACHMENT, gl_TEXTURE_2D, depth_texture, 0)
		gl_error = glGetError
		assert gl_error == gl_NO_ERROR else print_error gl_error

		# Check if the framebuffer is complete and valid
		assert glCheckFramebufferStatus(gl_FRAMEBUFFER) == gl_FRAMEBUFFER_COMPLETE

		# Take down
		glBindTexture(gl_TEXTURE_2D, 0)
		glBindFramebuffer(gl_FRAMEBUFFER, 0)
		gl_error = glGetError
		assert gl_error == gl_NO_ERROR else print_error gl_error
	end

	var destroyed = false

	fun destroy
	do
		if destroyed then return
		destroyed = true

		# Free the buffer
		glDeleteBuffers([buffer_array])
		var gl_error = glGetError
		assert gl_error == gl_NO_ERROR else print_error gl_error
		buffer_array = -1

		# Free the array and framebuffer plus its attachments
		glDeleteBuffers([buffer_array])
		glDeleteFramebuffers([light_view_framebuffer])
		glDeleteTextures([depth_texture])
	end
end