Friday, September 23, 2011

DDTe3 Hour 12 - 14 Hex Tile

This is a continuation of my series of articles on the creation of Dozen Days of Tiles episode 3. In this part, we continue developing the hex code by creating a hex-shaped image clipping tile.

As I don’t already have any existing classes for drawing masked shapes, a new class is going to need to be created for drawing the hex tile. This new class works very similarly to the existing ImageLayer class, but with a bit more drawing complexity. Overridding the ImageLayer class does not make sense as the drawing code is going to have to be replaced.

Clipping in the HTML5 canvas is a bit tricky. The important thing to remember about clipping is that you MUST save the state of the canvas before setting a clipping region and restore the state of the canvas once you are done. The canvas does not let you create a new clipping region larger than the existing region.  Each successive clip results in a ever-shrinking drawable region. I personally would have used a additive/subtractive model for building a clipping layer, but that is not what we currently have to work with.

Drawing the hex tile then consists of saving the canvas state, creating a hex path (outPath) for the tile, clipping the canvas using the path, drawing the tile as a rectangle, then restoring the canvas state. As I was doing all this drawing work anyway, I started thinking that perhaps I should combine the drawing of the hex with the drawing of the highlight/border.  Adding the setup/management methods of the TileBorder class to the HexTile class was simple as these classes for just set up variables. The hard part would be drawing them, and this was actually not overly difficult.

My first thought was to use a clipping approach as was done with the drawing of the image. This thought only lasted a few second as I quickly realized that instead of drawing a transparent rectangle over a clipping path, I could just draw a transparent color using the path. By creating the inner bounds of the border, I would also have the path needed for drawing the highlight color. With inner and outer hexes, it is possible to create the border path. As explained in the previous post, the border has to reverse the order of the inner path points as the winding order of the lines in the path determine the fill area. With the outer and inner hex path, this is very simple to do.

       for (var cntr = 0; cntr < 7; ++cntr) {
           this.borderPath[cntr] = this.outPath[cntr];
           this.borderPath[13-cntr] = this.inPath[cntr];
       this.borderPath[14] = this.outPath[6];

The next step then is to create a hex view. That, along with the first hex game, is what we will be looking at next.

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