Scratchcard

[Johan Schaep]

I am looking at the scratchcard solution and when ‘playing’ with the blocks there is one thing I still do not understand.

Color of the canvas layer above the picture is white (255-255-255) and by scratching you remove this white canvas color layer based on the fourth component of the white color which is set to 0.

I just don’t understand why it doesn’t work with another color e.g. red layer and setting the canvas color to scratch at 255-0-0 should work (analogous to the solution with white) but it doesn’t.

For me this is not logic.

Hope you can clarify!

[TimAI2]

A link to the "scratchcard solution" might help ?

[SteveJG]

Is Taifun's mini tutorial Scratch card what you are asking about Johan?  How to create a Scratchcard with App Inventor

The fourth 'color' 0 means the 'color' is set to transparent.

Colors are built  like this http://appinventor.mit.edu/explore/ai2/support/blocks/colors     If you add a fourth parameter, it controls the transparency.

Regards,

Steve

[Johan Schaep]

Right SteveJG. But try this solution for another color and it doesn't work, which I don't understand. In other words: how to make a scratchcard in a colour different from white?

@TimAI2: the link is indeed the link that SteveJG has given:

https://www.google.com/url?q=https%3A%2F%2Fpuravidaapps.com%2Fsnippets.php%232scratchcard&sa=D&sntz=1&usg=AFQjCNFP0ZVRwLGgDVh6bGpPeo4N4NEzfQ

[SteveJG]

Is this what you mean?

You want to change the Canvas.Background color.  This works.   Sorry, I do not understand your description about what you think should happen, but does not.  Why not provide an example Johan?   Show an image of the Blocks you tried.

Regards,

Steve

[Johan Schaep]

OK Steve, many thanks. And sorry but not used to be on forums...

Your solution works:

I was thinking in a too difficult way, although I still don't understand why the solution below does not work. I try to understand too much...