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Image Painting in Freehand Drawing Library

January 20, 2012

A bonus project is going out to all Freehand Drawing Library beta users this morning.  Currently, the library contains one fixed-width stroke with three drawing engines and three line decorators.  One question arose about how to create different strokes and the role of engines within the architecture.  I also received a comment about an iPad drawing app. that allowed people to ‘stamp’ or ‘paint’ smooth strokes with images.

Having an artist create any variety of cool images in Flash is a no-brainer.  The question is how to stamp that image repeatedly along a smooth stroke.  The answer provides a perfect illustration of stroke creation in the Freehand Drawing Library.  A stroke is designed based on certain desired characteristics, in this case the ability to distribute images along a smooth path.  A stroke engine (that implements IDrawingEngine) is created to match the general characteristics of a stroke.  Not all engines are compatible with all strokes, and that’s fine.

A StampedStroke class (implementing IFreehandDrawable, so it can be used in a Factory) was developed for the desired purpose.  A single engine, Stamp, computes the same smoothed stroke coordinates as the SmoothedStroke engine.  Since nothing is drawn into any graphics context, the concept of line decorators does not apply.  The stroke engine directly instantiates the image symbol and adds it to the display list.

The Stamp engine accepts a single engine parameter, ‘imagestamp’, which is the reference to the symbol created in Flash and exported with a base class that extends MovieClip.  Using the stroke is as simple as instantiation,

private var __stroke:StampedStroke  = new StampedStroke();
private var __data:StrokeDataVO = new StrokeDataVO();

Make sure the stroke engine and symbol are compiled into the SWF,

import net.algorithmist.freehand.StampedStroke;
import net.algorithmist.freehand.symbols.Starburst;

private static const STAMP_ENGINE:Class = Stamp;
private static const STAR_CLASS:Class = Starburst;

Then, inject stroke engine and assign engine parameters,

__data.drawingEngine = “net.algorithmist.freehand.engine.Stamp”;
__data.engineParams = {imagestamp:”net.algorithmist.freehand.symbols.Starburst”};

Assign the data provider for the stroke,

__stroke.data = __data;

Draw, and have fun.  The Stamp engine contains a back door to animating the stroke while it’s being drawn.  I may create an online example since it’s pretty cool🙂

The library is currently in the final beta phase before RC1.  Because of all the new capability, I’ve opened up several beta slots.   There is a small, three-figure license fee, which is a one-time cost.  All beta testers get free upgrades for life!

Please contact me at theAlgorithmist [at] gmail [dot] com if interested.

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