ALPHA MASK EFFECTS

RPG Maker XP

Alpha masking effects for bitmaps

  • orochii
  • 11/13/2018 03:43 PM
  • 865 views
RGSS1, tested with RGSS102J.dll (should work with RGSS2 and 3 too a.k.a. VX/Ace).

INTRODUCTION
I started doing modifications to a friend's DLL code, and I ended up doing this. Basically, it's a transparency effect. It includes a basic masking for any bitmap by using another bitmap's alpha channel, as well as a more complicated and somewhat powerful scrollable alpha masking using RGB components as alpha layers. It's kind of complicated to explain, but it lets you make something like this.



To the left, a sprite with some kind of animated outline. To the right, a single background with both scrolling alpha and static alpha layers.

CODE
Please download the following package!
http://share.cherrytree.at/showfile-31871/ozwbitmapextensions.zip
Right now all comments are in Spanish, I need to reupload it in English later. This download includes the necessary DLL, the source code for the DLL, and the wrapping code for using it in RGSS. It also includes an implementation for its easy use with Sprite. Something pretty similar can be done with Plane, but I haven't made it. You're free to do so.

COMPILING THE DLL
Any IDE should work, but just as reference I used Code::Blocks along with the GCC compiler that comes with it (version 4.7.1 if I recall correctly). Just install and open Code::Blocks, create a DLL project from it, throw the code there and you're good to go.

INSTRUCTIONS
New properties for Sprite class:
- @sprite.alpha_mask : a bitmap to be used as alpha mask.
- @sprite.alpha_mask_kind : 0 for simple mode, 1 for composite mode.
- @sprite.alpha_mask_sx : horizontal scrolling speed for the scrolling layer.
- @sprite.alpha_mask_sy : vertical scrolling speed for the scrolling layer.

AVAILABLE METHODS
Use these arbitrarily with any bitmap in order to apply alpha masking effects.
OZWBitmapExtension.simpleMask(srcBitmap, maskBitmap, targetBitmap)

srcBitmap : Source bitmap.
maskBitmap : Bitmap used for masking (multiplying alpha per pixel).
targetBitmap : The resulting bitmap will be stored here. Keep in mind, source and target must be the exact same size.

OZWBitmapExtension.compositeMask(srcBitmap, maskBitmap, targetBitmap, sx, sy)

srcBitmap : Source bitmap.
maskBitmap : Bitmap used for masking (resulting alpha = srcAlpha * (red * green + blue)).
targetBitmap : The resulting bitmap will be stored here. Keep in mind, source and target must be the exact same size.
sx : Horizontal displacement for the G layer.
sy : Vertical displacement for the G layer.


BUILDING A COMPOSITE MASK
A composite mask uses the R G and B channels sepparately for different effects. Each one of them have simple but very distinct properties.
R is the base alpha mask.
G is multiplied by R, which means if an spot in G is zero, it will result in zero.
B is added to R*G, which means it works as a threshold.

Another thing to keep in mind is that G can be scrolled by manipulating sx and sy at the compositeMask method. This is done automatically while updating the sprite by using the property implementation.

Here is an example of the alpha mask used for one of the examples above.
->


The image to the right consists of three grayscale images (shown to the left), joined together as a single image, each in a different color channel (in the order Red, Green and Blue). Use Photoshop or GIMP or any program with the option to manipulate sepparate channels in order to do this.

LICENSE
MIT License.

Have a nice day. :^)