Is there a way to apply an alpha mask to a FlxCamera?

Question

I'm trying to implement this camera but one of the obstacles I'm facing right now, is the merging of two cameras (what he describes here).

At first I tried to make a non-rectangular camera, but I don't think it's possible without changing a lot of things in the way HaxeFlixel renders.

And then I found the alphaMask() function in the FlxSpriteUtil package and I think it would be a better solution. Not only would it solve my problem, it would actually permit all kinds of funky-shaped cameras, you just have to create the right mask!

But the new problem is that I don't know how to (and again, if it's possible without changing a bit the FlxCamera) apply it to the camera.

Internally, the FlxCamera might use a FlxSprite, but only in blit render mode, and I am in tiles render mode (haven't found how to change, not good enough solution in my opinion), which uses a Flash Sprite instead and I don't know what to do with it.

So in short, do you have an idea how to apply an AlphaMask to a FlxCamera? Or another way to achieve what I'm trying to do?

PS: If you want to have a look at the (ugly and frenchly commented) code, it's over here!

Answer 1

You can render the contents of a FlxCamera to a FlxSprite (though it does require conditional code based on the render mode). The TurnBasedRPG tutorial game uses this for the wave effect in the combat screen, see CombatHUD.hx:

if (FlxG.renderBlit)
    screenPixels.copyPixels(FlxG.camera.buffer, FlxG.camera.buffer.rect, new Point());
else
    screenPixels.draw(FlxG.camera.canvas, new Matrix(1, 0, 0, 1, 0, 0));

Here's a code example that uses this to create a HaxeFlixel-shaped camera:

package;

import flixel.tweens.FlxTween;
import flash.geom.Matrix;
import flixel.FlxCamera;
import flixel.FlxG;
import flixel.FlxSprite;
import flixel.FlxState;
import flixel.graphics.FlxGraphic;
import flixel.system.FlxAssets;
import flixel.util.FlxColor;
import openfl.geom.Point;
using flixel.util.FlxSpriteUtil;

class PlayState extends FlxState
{
    static inline var CAMERA_SIZE = 100;

    var maskedCamera:FlxCamera;
    var cameraSprite:FlxSprite;
    var mask:FlxSprite;

    override public function create():Void
    {
        super.create();

        maskedCamera = new FlxCamera(0, 0, CAMERA_SIZE, CAMERA_SIZE);
        maskedCamera.bgColor = FlxColor.WHITE;
        maskedCamera.scroll.x = 50;
        FlxG.cameras.add(maskedCamera);

        // this is a bit of a hack - we need this camera to be rendered so we can copy the content
        // onto the sprite, but we don't want to actually *see* it, so just move it off-screen
        maskedCamera.x = FlxG.width;

        cameraSprite = new FlxSprite();
        cameraSprite.makeGraphic(CAMERA_SIZE, CAMERA_SIZE, FlxColor.WHITE, true);
        cameraSprite.x = 50;
        cameraSprite.y = 100;
        cameraSprite.cameras = [FlxG.camera];
        add(cameraSprite);

        mask = new FlxSprite(FlxGraphic.fromClass(GraphicLogo));

        var redSquare = new FlxSprite(0, 25);
        redSquare.makeGraphic(50, 50, FlxColor.RED);
        add(redSquare);
        FlxTween.tween(redSquare, {x: 150}, 1, {type: FlxTween.PINGPONG});
    }

    override public function update(elapsed:Float):Void
    {
        super.update(elapsed);

        var pixels = cameraSprite.pixels;
        if (FlxG.renderBlit)
            pixels.copyPixels(maskedCamera.buffer, maskedCamera.buffer.rect, new Point());
        else
            pixels.draw(maskedCamera.canvas);

        cameraSprite.alphaMaskFlxSprite(mask, cameraSprite);
    }
}