Physics debug

Setup

With the physics visualization on, all collision object shapes are visible. In addition, at intersections the normals at the collision points are shown.

The example collection consists of:

4 blocks with dynamic collision objects with Restituion 1.0, so they bounce forever,
4 walls with static collision objects forming boundaries for the blocks,
game object go with:
- label with example description,
- a script physics.script included below.

physics debug

This collection is additionally loaded via a Collection Proxy component in main.collection. Therefore, sending message set_time_step to its url "main:/loader#physicsproxy" is causing the proxy to have a different update time, causing e.g. the slow-motion effect, which might be helpful when debugging physics.

collection proxy

Scripts

physics.script

function init(self)
    msg.post(".", "acquire_input_focus") -- <1>
    self.show_debug = false -- <2>
end

function on_input(self, action_id, action)
    if action_id == hash("touch") and action.pressed then
        msg.post("@system:", "toggle_physics_debug") -- <3>
        if self.show_debug then -- <4>
            msg.post("main:/loader#physicsproxy", "set_time_step", { factor = 1, mode = 0 })
        else
            msg.post("main:/loader#physicsproxy", "set_time_step", { factor = 0.1, mode = 1 })
        end
        self.show_debug = not self.show_debug -- <5>
    end
end

--[[
1. Make sure this game object's script component gets input from the engine.
2. A state flag to track if we show debug info or not.
3. If user clicks, toggle physics visualization.
4. In addition, we want to set the timestep. That is done through the collection proxy that loaded this example. Since we cannot get hold of the proxy from this side of it we message the loader game object in the main collection and it will relay the message to the proxy component.
5. Switch the `show_debug` flag.
--]]

loader.script

function init(self)
    msg.post(".", "acquire_input_focus")
    msg.post("#physicsproxy", "load")
end

function on_message(self, message_id, message, sender)
    if message_id == hash("proxy_loaded") then
        msg.post(sender, "init")
        msg.post(sender, "enable")
    end
end

This example was created by Defold Foundation.

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