Added support for shaders in FlxStrip and FlxDrawTrianglesItem

[UncertainProd]

This pr adds support for shaders with the FlxStrip class.
When I was working with the FlxStrip class I noticed that setting its shader property or alpha property did not have any effect on it, while it did work on regular FlxSprites. It looks like it's because FlxCamera.drawTriangles does not take in any parameters related to them, so I added those in this pr.

Example code:

package;

import flixel.FlxG;
import flixel.FlxSprite;
import flixel.FlxState;
import flixel.FlxStrip;
import flixel.graphics.tile.FlxDrawTrianglesItem.DrawData;
import flixel.system.FlxAssets.FlxShader;
import flixel.util.FlxColor;

class PlayState extends FlxState
{
	var shaderStrip:FlxStrip;
	var alphaStrip:FlxStrip;
        var normalsprite:FlxSprite;

        var simpleShader:GreenShader;
	override public function create()
	{
		super.create();

		shaderStrip = new FlxStrip(50, 50);
		shaderStrip.makeGraphic(100, 100, FlxColor.YELLOW);
		shaderStrip.vertices = DrawData.ofArray([100.0, 100.0, 150, 100, 125, 150]);
		shaderStrip.indices = DrawData.ofArray([0, 1, 2]);
		shaderStrip.uvtData = DrawData.ofArray([0, 0, 0, 1, 1, 1.0]);
		shaderStrip.shader = new GreenShader();
		add(shaderStrip);

                alphaStrip = new FlxStrip(0, 0);
		alphaStrip.makeGraphic(100, 100, FlxColor.RED);
		alphaStrip.vertices = DrawData.ofArray([300.0, 100.0, 350, 100, 325, 150]);
		alphaStrip.indices = DrawData.ofArray([0, 1, 2]);
		alphaStrip.uvtData = DrawData.ofArray([0, 0, 0, 1, 1, 1.0]);
		add(alphaStrip);

		normalsprite = new FlxSprite(0, 0).makeGraphic(100, 100, FlxColor.BLUE);
		normalsprite.shader = new GreenShader();
		add(normalsprite);
	}

	override function update(elapsed:Float)
	{
		if(FlxG.keys.pressed.A)
		{
			alphaStrip.alpha -= 0.01;
		}
		if(FlxG.keys.pressed.D)
		{
			alphaStrip.alpha += 0.01;
		}
		super.update(elapsed);
	}
}

class GreenShader extends FlxShader
{
	@glFragmentSource('
	#pragma header

	void main()
	{
		vec4 clr = texture2D(bitmap, openfl_TextureCoordv);
		gl_FragColor = vec4(0.0, 1.0, 0.0, 1.0) * clr.a;
	}
	')
	public function new()
	{
		super();
	}
}

When I tested this on windows and html5 it worked

[Geokureli]

Thanks for the example, I'll try to get to this soon

[Geokureli]

looks like it's failing on flash. You don't need to go out of your way to make this feature work in flash, but you do need to use #if flash checks to prevent compile errors on flash

[UncertainProd]

Alright, I added in those checks

[Geokureli]

thanks, will check this manually soon

[Geokureli]

This rules! Thanks, UncertainProd.

This was my edited test example:
https://github.com/Geokureli/flixel-tests/blob/main/Source/states/FlxStripShaderTestState.hx