Add coordinate conversion helper for GUI picking, & demo script (#14)

- Credit to subsoap / Pkeod for commissioning this feature.

game/lowrezjam/hover_hud_heart.gui_script

@@ -0,0 +1,32 @@
+
+-- A sample script to demonstrate GUI node hovering with the mouse.
+
+local coords = require "lowrezjam.render.coords"
+
+function init(self)
+	msg.post(".", "acquire_input_focus")
+	self.hearts = {}
+	for i=1,3 do
+		self.hearts[i] = gui.get_node("life"..i)
+	end
+end
+
+local function update_hover(self, x, y)
+	local hit_i, hit_heart
+	for i,heart in ipairs(self.hearts) do
+		if gui.pick_node(heart, x, y) then
+			gui.set_alpha(heart, 0.5)
+			hit_i, hit_heart = i, heart
+		else
+			gui.set_alpha(heart, 1)
+		end
+	end
+	return hit_i, hit_heart
+end
+
+function on_input(self, action_id, action)
+	if not action_id then
+		local px, py = coords.action_to_gui_pick(action.x, action.y)
+		update_hover(self, px, py)
+	end
+end

game/lowrezjam/hud.gui

@@ -1,4 +1,4 @@
-script: ""
+script: "/game/lowrezjam/hover_hud_heart.gui_script"
 fonts {
   name: "pixelfont"
   font: "/lowrezjam/fonts/pixelfont.font"

lowrezjam/render/coords.lua

@@ -0,0 +1,57 @@
+
+-- A module for converting mouse coordinates to GUI coordinates for checking collision with GUI nodes.
+
+local M = {}
+
+local proj_w = sys.get_config_int("display.width", 960)
+local proj_h = sys.get_config_int("display.height", 640)
+
+M.window_width, M.window_height = proj_w, proj_h
+M.game_width = 64
+M.game_height = 64
+M.scale_snap = true
+
+local function get_zoom()
+	local zoom = math.min(M.window_width / M.game_width, M.window_height / M.game_height)
+	if M.scale_snap then
+		zoom = math.max(1, math.floor(zoom))
+	end
+	return zoom
+end
+
+local function get_offset(zoom)
+	local w, h = M.game_width * zoom, M.game_height * zoom
+	return (M.window_width - w)/2, (M.window_height - h)/2
+end
+
+function M.action_to_screen(ax, ay)
+	local sx = (ax / proj_w) * M.window_width
+	local sy = (ay / proj_h) * M.window_height
+	return sx, sy
+end
+local action_to_screen = M.action_to_screen
+
+function M.screen_to_action(sx, sy)
+	local ax = sx * proj_w / M.window_width
+	local ay = sy * proj_h / M.window_height
+	return ax, ay
+end
+local screen_to_action = M.screen_to_action
+
+function M.action_to_gui_pick(ax, ay)
+	local sx, sy = action_to_screen(ax, ay) -- It's way less confusing to work in real screen coords.
+
+	local action_width, action_height = screen_to_action(M.game_width, M.game_height) -- Bottom left of gui is always at 0, 0.
+	local scalex, scaley = action_width/M.game_width, action_height/M.game_height
+
+	local zoom = get_zoom()
+	local ox, oy = get_offset(zoom)
+
+	local x = (sx - ox)/zoom -- Zero to `width` inside canvas area.
+	local y = (sy - oy)/zoom -- Zero to `height` inside canvas area.
+	x, y = x * scalex, y * scaley
+
+	return x, y -- NOTE: Not rounded to even pixels.
+end
+
+return M

lowrezjam/render/lowrez.render_script

@@ -6,10 +6,13 @@ local SET_SIZE = hash("set_size")
 
 local IDENTITY = vmath.matrix4()
 
+local coords = require "lowrezjam.render.coords"
+
 local function setup(self, width, height)
 	self.width = width
 	self.height = height
 	self.lowrez_projection = vmath.matrix4_orthographic(0, width, 0, height, -1, 1)
+	coords.game_width, coords.game_height = width, height
 
 	-- render target buffer parameters
 	local color_params = {
@@ -70,6 +73,10 @@ function init(self)
 
 	self.upscale_material = hash("lowrez")
 	self.scale_snap = true
+	coords.scale_snap = true
+	local window_width = render.get_window_width()
+	local window_height = render.get_window_height()
+	coords.window_width, coords.window_height = window_width, window_height
 end
 
 
@@ -154,7 +161,10 @@ local function draw_controls(self)
 end
 
 function update(self)
-	clear(self,	render.get_window_width(), render.get_window_height())
+	local window_width = render.get_window_width()
+	local window_height = render.get_window_height()
+	coords.window_width, coords.window_height = window_width, window_height
+	clear(self, window_width, window_height)
 	render.enable_render_target(self.rt)
 	draw_game(self)
 	render.disable_render_target(self.rt)
@@ -175,6 +185,7 @@ function on_message(self, message_id, message)
 		else
 			self.scale_snap = true
 		end
+		coords.scale_snap = self.scale_snap
 	elseif message_id == SET_SIZE then
 		setup(self, message.width, message.height)
 	end