This is a step by step guide on creating a mask for use in adventure game studio from photoshop (cs5 but it should work with older versions), importing the mask and changing the image size.
Firstly, Open your image.
You may want to change the size to make sure it will be suitable in AGS
Go to image/ Image Size then change it something suitable. It's easier if you have it set to pixels.
Next hide or delete any of the layers you do not want to use, the eye symbol next to each layer or right click delete layer or even use the bin icon.
Next select a layer or a group, if it's a group right click, then merge group
Then right click and select stroke, or select it from the fx button at the bottom of your tool bar.
once on the stoke layer style set it to max 250 and inside the colour doesn't really matter at this stage
Do this for each layer and you should end up with something like this
use this colour code: a6caf0 I just found it the easiest to make masks with it
Then paint bucket over all your layers using this colour
The go to mode/ indexed color
Change it to system windows
Then when you come to save it make sure it's a bmp
and 8 bit is the only option viisible ( it should also have mentioned 256 colour earlier.)
Now putting it in engine, load up your level, select the import mask from file option.
This error message will appear if it's a different error message it maybe hasn't worked properly.
Then the mask should be visible like this
Then just fill in the mask with the paint bucket and if it's a walk behind area drag the line down into the appropriate place. This level will have many separate walk behind areas.
This is my first tutorial hope it helped
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