How to know if i'm pressing in the alpha channel of a sprite

Krakatoa

I have rounded buttons with irregular areas.

¿How can I check if i'm pressing in the alpha channel to discard the click?

This is my code:

StartMenu = Core.class(Sprite)
local logo_background = Bitmap.new(Texture.new("background.png"))
local start_button = Bitmap.new(Texture.new("SM_start.png"))

function StartMenu:init()
logo_background:setScale(0.96, 1.04)
self:addChild(logo_background)
self:addChild(start_button)
start_button:addEventListener(Event.MOUSE_DOWN, self.startGame, self)
end

function StartMenu:startGame(event)
if start_button:hitTestPoint(event.x, event.y) then
start_button.isFocus = true
end
end


Inside the startGame i want to check if the click is in the alpha zone to discard it.
I think one way is to access to the pixel clicked but I don't how to acces to that info.

Disciple

As far as I know (through some research I did back when I had this same doubt) this is not available in Gideros as you mention it.

However, there's a related discussion in this thread below that has some code to get around it:
http://giderosmobile.com/forum/discussion/218/how-to-get-spritehittestpoint-to-ignore-transparent-areas-of-image#Item_1

talis

If you have a non rectangle button (close to circle) you can handle like this. Once i had the same issue.
http://giderosmobile.com/forum/discussion/3595/non-rectangle-button#Item_7

ar2rsawseen

Currently reading pixel value in Gideros is (although possible bu) very unefficient and unhandy
And it is much more efficient to use mathematical solutions, to check if point is inside the shape.

Krakatoa

Finally I discarted to do this because I don't need such precision considering the application will be ruled in mobile phones. I'm playing with box2d and I think it's easy to make a polyline if I want to know if a irregular entity it's clicked or not. By now I won't use it.

Thank you

SinisterSoft

You could use a collision 'grid' or mask, that you look at if you fall within the w/h boundry of the shape's box. The problems occur if you use scaling or rotation (or any other effect that warps the size, shape of things).