Problem with rendering depth map

Questions
1

I am trying to recreate the rendered depth map from this Learn OpenGL tutorial but when running the project, the depth map renders very briefly at the beginning before the whole screen goes blank. I’ve been trying to figure out the reason for this bug. I would appreciate any help I can get to figure this out. Thanks in advance.

Here’s the render script:

local function create_depth_buffer(w, h)
	local color_params = {
		format = graphics.TEXTURE_FORMAT_RGBA,
		width = w,
		height = h,
		min_filter = graphics.TEXTURE_FILTER_NEAREST,
		mag_filter = graphics.TEXTURE_FILTER_NEAREST,
		u_wrap = graphics.TEXTURE_WRAP_REPEAT,
		v_wrap = graphics.TEXTURE_WRAP_REPEAT
	}

	local depth_params = {
		format = graphics.TEXTURE_FORMAT_DEPTH,
		width = w,
		height = h,
		min_filter = graphics.TEXTURE_FILTER_NEAREST,
		mag_filter = graphics.TEXTURE_FILTER_NEAREST,
		u_wrap = graphics.TEXTURE_WRAP_REPEAT,
		v_wrap = graphics.TEXTURE_WRAP_REPEAT
	}

	return render.render_target("shadow_buffer", {[graphics.BUFFER_TYPE_COLOR0_BIT] = color_params, [graphics.BUFFER_TYPE_DEPTH_BIT] = depth_params })
end

function init(self)
	self.model_pred = render.predicate({"model"})
	self.shadow_debug_pred = render.predicate({"shadow_debug"})

	-- lighting info
	self.z_buffer = create_depth_buffer(1024, 1024)
	self.light_pos = vmath.vector3(2, 4, -1)
end

local frame = 0
local function clear_buffers()
	render.clear({[graphics.BUFFER_TYPE_COLOR0_BIT] = vmath.vector4(0.1, 0.1, 0.1, 0.1), [graphics.BUFFER_TYPE_DEPTH_BIT] = 1})
end

local function render_depth_to_rt(self)
	-- Set the render targer (framebuffer).
	render.set_render_target(self.z_buffer)
	render.set_viewport(0, 0, 1024, 1024)

	--clear_buffers()
	render.clear({[graphics.BUFFER_TYPE_COLOR0_BIT] = vmath.vector4(0.1, 0.1, 0.1, 0.1), [graphics.BUFFER_TYPE_DEPTH_BIT] = 1})

	-- enable depth buffer for writing
	render.set_depth_mask(true)
	render.enable_state(graphics.STATE_DEPTH_TEST)

	-- render depth of scene to texture from the light's perspective
	local mtx_light_proj, mtx_light_view, mtx_light_space_matrix
	local near_plane, far_plane = 1, 7.5
	mtx_light_proj = vmath.matrix4_orthographic(-10, 10, -10, 10, near_plane, far_plane)
	mtx_light_view = vmath.matrix4_look_at(self.light_pos, vmath.vector3(), vmath.vector3(0, 1, 0))
	mtx_light_space_matrix = mtx_light_proj * mtx_light_view

	local mtx_constants = render.constant_buffer()
	mtx_constants.mtx_light_space_matrix = mtx_light_space_matrix

	-- draw the predicate with the simple depth shader
	render.enable_material("simple_depth")

	render.draw(self.model_pred, {constants = mtx_constants})

	render.disable_material()

	render.disable_state(graphics.STATE_DEPTH_TEST)
	render.set_depth_mask(false)

	-- set the render target back to default
	render.set_render_target(render.RENDER_TARGET_DEFAULT)

end

local function render_rt_to_screen(self)
	render.set_viewport(0, 0, render.get_window_width(), render.get_window_height())

	clear_buffers()
	
	render.set_view(vmath.matrix4())
	render.set_projection(vmath.matrix4())

	--local plane_constants = render.constant_buffer()
	--plane_constants.near_far_planes = vmath.vector4(1, 7.5, 0, 0)

	render.enable_texture(0, self.z_buffer, graphics.BUFFER_TYPE_COLOR0_BIT)
 	render.draw(self.shadow_debug_pred)--, {constants = plane_constants})

 	render.disable_texture(0)
end

function update(self, dt)
	-- debugging
	frame = frame + 1
	--clear_buffers("update")

	render_depth_to_rt(self)
	render_rt_to_screen(self)
end

Here’s the project

Depth Map Render.zip (2.2 MB)