Rotation issue While Reflected (2D Platform Game) - actionscript-3

My player's arm is programmed to follow my mouse and rotate accordingly and I've programmed bullets to be fired using this rotational value
(Math.atan2(this._dy, this._dx) * 180 / Math.PI
where _dy is the y location of the mouse (-) the y of my player's arm and the _dx is the x location of mouse (-) the y of my player's arm.
However, when I program the player to reflect when the mouse has crossed the x-coordinates, the bullet angle is also reflected. How would I fix this issue?
I've already tried subtracting 180 from the angle but it still doesn't fire towards the direction of the mouse.

First, make sure you have this parent-child-sibling relationship:
"A" should be the parent of "B" and "C". "B" and "C" should have no direct link. Their connection is that they have the same parent. So when you want to move the character, move the parent, and both will move. Now, for the good stuff:
Use key frames and sibling relationship
beginner level approach
Make the character and the arm both children of the same parent display object container (Movie Clip in this case). Now, instead of flipping anything by xScale, which I assume you did, you can just have both MC children (arm and character) go to frame 2 (or whatever is available) where the graphics are flipped.
xScale body, move arm to frame 2, change z order
moderate level approach (best result)*
Alternatively, you could do that same "sibling" setup as above, and then scale the character but not the arm (I think scaling the arm will mess it up again, but you could have the arm go to frame 2 and have it drawn reversed so the thumb and handle are pointing the right way. Bonus points for changing the z stacking order so the arm goes to the other side of the body. xScale for only the body allows you to only have one set of frames for animation of his legs and torso etc. but also avoid scaling the arm at all).
Global properties
advanced approach
A third option is to use global rotation and global points. I won't illustrate that here because I'm not that advanced and it would take me a while to figure out the exact syntax. If you already have mastered global properties, try this; if not, try one of the ones above.
* Example (best result)
if (facingRight == true && stage.mouseX < totalChar.x){
// totalChar is on the stage
// and contains two children:
// armAndGun and bodyHeadLegs
totalChar.armAndGun.gotoAndStop(2);
// in frame 2 of the arm MC, draw the
// arm and gun in the flipped orientation
totalChar.addChild(bodyHeadLegs);
// re-ads body to parent so it's
// z-order is above the arm;
totalChar.bodyHeadLegs.xScale = -1;// flips body and any animation of legs and head
facingRight = false;
// use a variable or property like this
// to keep him from constantly flipping
}
You'll need similar code to flip him back the other way.

Related

ActionScript 3 Simple Projectile Pathing

Good evening (at the time of writing)
The research I've done on this topic has turned up numerous fruitful code blocks regarding various situations similar to mine, but not quite identical. If one exists which I have not uncovered, I would be grateful for a link!
I have a few pertinent criteria, all on a 2d plane, and the question is related to 2d projectile pathing:
1) Object A: position ax,ay
2) Object B: position bx, by
3) Object P: (projectile) origin position bx,by
Object P leaves object B's X/Y position at a static velocity, traveling toward object A's X/Y position.
Objects A and B continue to move along their paths, irrespective of object P's trajectory. Object P continues to move from ax,ay to bx,by and beyond. I think I just need the angle and velocity, and don't need to continue to track beyond that (just increment movement steps accordingly till off-stage, where the object is disposed).
I'm working in Actionscript 3, any help would be greatly appreciated. Thanks!
In most case in 2D x-y plane, it is usually easier to handle movement and momentum in planar(separate in x-axis and y-axis) fashion than polar(angle+distance) fashion. I couldn't get the exact behaviour of projectile you want, so I assume you want a simple, dumbfire-rocket style projectile (which keeps initial direction).
:: 1. Projectile initiation ("Firing" of projectile)
var duration:int //(duration of flight(until getting to (ax,ay) described in number of frames)
var spdX:Number //(x-axis part of speed, described in pixels per frame)
var spdY:Number //(y-axis part of speed, described in pixels per frame)
spdX=(bx-ax)/duration;
spdY=(by-ay)/duration;
:: 2. Projectile movement (listen to ENTER_FRAME Event, executed once per frame)
projectile.x+=spdX;
projectile.y+=spdY;
:: if you want to change velocity of projectile, simple multiplication will handle it.
public function adjustSpeed(ratio:Number):void
{
spdX*=ratio;
spdY*=ratio;
}

What's the purpose of Canvas.Context Save and Restore in this example?

This page shows some animations in HTML5 canvas. If you look at the source of the scroller, there's a statement to save the context after clearing the rectangle and restoring it after the animation. If I substitute the restore statement with another ctx.clearRect(0, 0, can.width, can.height statement, nothing works. I thought the restore is restoring the cleared rectangle but it seems its restoring more info. What's that extra info that's needed for the next frame?
I am not looking for HTML5 textbook definitions of Save and Restore but I want to understand why they are needed in this specific example.
UPDATE
It's frustrating to get an answer where I specifically already mentioned in the question I don't want to get the definitions of save() and restore(). I already know Save() saves the state of the context and Restor()e restores it. My question is very specific. Why is restore() used in the manner in the example when all the Save did is saved an empty canvas. Why is restoring an empty canvas not the same as clearing it?
Canvas state isn't what's drawn on it. It's a stack of properties which define the current state of the tools which are used to draw the next thing.
Canvas is an immediate-mode bitmap.
Like MS Paint. Once it's there, it's there, so there's no point "saving" the current image data, because that would be like saving the whole JPEG, every time you make a change, every frame...
...no, the state you save is the state which will dictate what coordinate-orientation, dimension-scale, colour, etc, you use to draw the NEXT thing (and all things thereafter, until you change those values by hand).
var canvas = document.createElement("canvas"),
easel = canvas.getContext("2d");
easel.fillStyle = "rgb(80, 80, 120)";
easel.strokeStyle = "rgb(120, 120, 200)";
easel.fillRect(x, y, width, height);
easel.strokeRect(x, y, width, height);
easel.save(); // stores ALL current status properties in the stack
easel.rotate(degrees * Math.PI / 180); // radians
easel.scale(scale_X, scale_Y); // any new coordinates/dimensions will now be multiplied by these
easel.translate(new_X, new_Y); // new origin coordinates, based on rotated orientation, multiplied by the scale-factor
easel.fillStyle = "gold";
easel.fillRect(x, y, width, height); // completely new rectangle
// origin is different, and the rotation is different, because you're in a new coordinate space
easel.clearRect(0, 0, width, height); // not even guaranteed to clear the actual canvas, anymore
easel.strokeRect(width/2, height/2, width, height); // still in the new coordinate space, still with the new colour
easel.restore(); // reassign all of the previous status properties
easel.clearRect(0, 0, width, height);
Assuming that you were only one state-change deep on the stack, that last line, now that your canvas' previous state was restored, should have successfully cleared itself (subpixel shenanigans notwithstanding).
So as you can see, it has very, VERY little to do with erasing the canvas.
In fact, it has nothing to do with erasing it, at all.
It has to do with wanting to draw something, and doing the basic outlining and sweeping colours/styles, and then manually writing in the colours for the smaller details on top, and then manually writing all of the styles back the way they were before, to go back to sweeping strokes for the next object, and on and on...
Instead, save general states that will be reused, create a new state for smaller details, and return to the general state, without having to hard-code it, every time, or write setter functions to set frequently-used values on the canvas over and over (resetting scale/rotation/affine-transforms/colours/fonts/line-widths/baseline-alignment/etc).
In your exact example, then, if you're paying attention, you'll see that the only thing that's changing is the value of step.
They've set the state of a bunch of values for the canvas (colour/font/etc).
And then they save. Well, what did they save?
You're not looking deep enough. They actually saved the default translation (ie: origin=0,0 in original world-space).
But you didn't see them define it?
That's because it's defined as default.
They then increase the step 1 pixel (actually, they do this first, but it doesn't matter after the first loop -- stay with me here).
Then they set a new origin point for 0,0 (ie: from now on, when they type 0,0 that new origin will point to a completely different place on the canvas).
That origin point is equal to x being the exact middle of the canvas, and y being equal to the current step (ie: pixel 1 or pixel 2, etc... and why the difference between starting at 0 and starting at 1 really doesn't matter).
Then what do they do?
They restore.
Well, what have they restored?
...well, what have they changed?
They're restoring the point of origin to 0,0
Why?
Well, what would happen if they didn't?
If the canvas is 500px x 200px, and it starts at 0,0 in our current screen space... ...that's great...
Then they translate it to width/2, 1
Okay, so now when they ask to draw text at 0,0 they'll actually be drawing at 250, 1
Wonderful. But what happens next time?
Now they're translating by width/2, 2
You think, well, that's fine... ...the draw call for 0,0 is going to happen at 250, 2, because they've set it to clear numbers: canvas.width/2, 2
Nope. Because current 0,0 is actually 250,1 according to our screen. And one translation is relative to its previous translation...
...so now you're telling the canvas to start at it's current-coordinates' 0,0 and go left 250, and down 2.
According to the screen (which is like a window, looking at the map, and not the map, itself) we're now 500px to the right, and 3 pixels down from where we started... And only one frame has gone by.
So they restore the map's coordinates to be the same origin as the screen's coordinates (and the rotation to be the same, and the scale, and the skew, etc...), before setting the new one.
And as you might guess, by looking at it, now, you can see that the text should actually move top to bottom. Not right to left, like the page says...
Why do this?
Why go to the trouble of changing the coordinate-system of the drawing-context, when the draw commands give you an x and y right there in the function?
If you want to draw a picture on the canvas, and you know how high and wide it is, and where you'd like the top-left corner to be, why can't you just do this:
easel.drawImage(myImg, x, y, myImg.width, myImg.height);
Well, you can.
You can totally do that. There's nothing stopping you.
In fact, if you wanted to make it zoom around the screen, you could just update the x and y on a timer, and call it a day.
But what about if you were drawing a game character? What if the character had a hat, and had gloved hands, and big boots, and all of those things were drawn separate from the character?
So first you'd say "well, he's standing at x and y in the world, so x plus where his hand is in relation to his body would be x + body.x - hand.x...or was that plus..."
...and now you have draw calls for all of his parts that are all looking like a notebook full of Grade 5 math homework.
Instead, you can say: "He's here. Set my coordinates so that 0,0 is right in the middle of my guy". Now your draw calls are as simple as "My right hand is 6 pixels to the right of the body, my left hand is 3 pixels to the left".
And when you're done drawing your character, you can set your origin back to 0,0 and then the next character can be drawn. Or, if you want to attempt it, you can then translate from there to the origin of the next character, based on the delta from one to the other (this will save you a function call per translation). And then, if you only saved state once the whole time (the original state), at the end, you can return to 0,0 by calling .restore.
The context save() saves stuff like transformation color among other stuff. Then you can change the context and restore it to have the same as when you saved it. It works like a stack so you can push multiple canvas states onto the stack and recover them.
http://html5.litten.com/understanding-save-and-restore-for-the-canvas-context/

MovieClip alignment (a character with multiple states) without using a meta-MovieClip

I'm working on a game where there are 4 characters on screen, each with several different states and corresponding MovieClips so that my library looks a little something like this:
Character 1:
IdleAnimation
SleepAnimation
..
Character 2:
IdleAnimation
SleepAnimation
..
Each animation (provided by a 3rd party) has a different anchor point, so when character A is at position 100, 100 on screen and moves from the idle to sleep animation he suddenly jumps 20 pixels to the right due to the anchor point.
Usually I would store all the different states in one MovieClip in separate frames and manually adjust the position of each one til they matched up, however I am also trying to port this to Android and therefore must keep the number of children on screen at once to a minimum.
Is there anything else I can do other than store offset x and y values for each character and each animation, and simple set the x/y via code whenever their state changes?
To keep the numChildren down I guess you have no choice
but to keep track of x- and y-offsets of the animations of each character
stored perhaps in an Object variable of form { state: registration_point }.
Then when changing states you can set the registration point
through this method by Emanuel Feronato:
http://www.emanueleferonato.com/2010/08/04/changing-a-movieclip-registration-point-on-the-fly-with-as3/
An idea to try though is to simply place the registration point to the center of each animation state:
var reg_x:Number = mc.width / 2;
var reg_y:Number = mc.height / 2;

AS3 - geometry - perspective projection of a point on a 2D plane

I'm currently struggling on a problem that seems far beyond my maths capacities (been a long time since I've made some proper maths...) and I would appreciate some help on that.
Here's my setting :
I got some simple shapes (rectangles), and I "project" their bottom points on a line, coming from an Origin point.
Up to this point everything is fine.
But now I'd like to draw the original shape distorted as if it was projected with some perspective on a plane.
Please consider that I have nothing related to any rotation, isometric or any 3D or fake 2D perspective in my code, I'm only trying to draw some shapes using the graphics library to only have a feeling of something real.
Here's a quick drawing of what I'm trying to do :
What I know :
Origin point coordinates
the rect position & sizes
the red line position
the A & B points coordinates
What I want to determine is the coordinates of the C & D points, thing that could be easy if I wasn't struggling to find the "Origin bis" coordinates.
What I'm trying to do is to fake the projection of my rectangle on something that can be considered as a "floor" (related to the plane where my original rectangle is that can be seen as a wall).
Maybe I'm over-complicating the problem or maybe I fail to see any other easier way to do it, but I'm really not good anymore in any geometry or maths thing... :-(
Thanks a lot for your answers !
hmm i don't know if I undestood it correctly but I think you have too few input parameters:
you said the following information is given:
Origin point coordinates
the rect position & sizes
the red line position
the A & B points coordinates
I don't think it is possible to get your projected rectangle with this information alone.
Additionally, I think your green lines and the 'origin Bis' aren't helpful as well.
Perhaps, try this:
Supose, a blue line going through the points C & D is given as well.
Then you could find your projected rectangle by projecting the top of the rectangle onto that blue line.
So in summary:
You define an origin + two parallel lines, a red and a blue one.
Then you can project the top of the rect onto the blue line and the bottom of the rect onto the red line, yielding the points A,B,C,D
I hope this helps.
If I'm right, this code will show what you wanted to see.
First of all, I've ignored your initial setup of objects and information, and focused on the example situation itself; fake-projecting shadow for a "monolith" (any object is possible with the example below, even textured)
My reason was that it's really quite easy with the Matrix class of ActionScript, a handy tool worth learning.
Solution:
You can use the built-in Matrix class to do skew transform on DisplayObjects.
Try this example:
(The "useful" part lies in the _EF EnterFrame handler ;) )
import flash.display.MovieClip;
import flash.geom.Matrix;
import flash.events.Event;
import flash.display.BitmapData;
const PIP180:Number = Math.PI / 180;
const MAX_SHADOW_HEIGHT_MULTIPLIER:Number = 0.25; // you can also calculate this from an angle, like ... = Math.sin(angle * PIP180);
const ANIM_DEG_PER_FRAME:Number = 1.0 * PIP180; // the shadow creeps at a +1 degree per frame rate
var tx:BitmapData = new MonolithTexture(); // define this BitmapData in the library
var skew:Number = -10 * PIP180; // initial
var mono:MovieClip = new MovieClip();
mono.graphics.beginBitmapFill(tx);
// drawn that way the registration point is 0,0, so it's standing on the ground
mono.graphics.drawRect(0, -tx.height, tx.width, tx.height);
mono.graphics.endFill();
// align monolith to the "ground"
mono.x = stage.stageWidth / 2;
mono.y = stage.stageHeight - 100;
// make it be 100x300 pixel
mono.width = 100;
mono.height = 300;
var shad:MovieClip = new MovieClip();
// colored:
shad.graphics.beginFill(0x000000);
// or textured:
//shad.graphics.beginBitmapFill(tx);
shad.graphics.drawRect(0, -tx.height, tx.width, tx.height);
shad.graphics.endFill();
addChild(shad); // shadow first
addChild(mono); // then the caster object
addEventListener(Event.ENTER_FRAME, _EF);
function _EF(e:Event):void {
// animate skew on the positive half circle
skew = (skew + ANIM_DEG_PER_FRAME) % Math.PI;
// Matrix takes 6 parameters: a, b, c, d, x, y
// for this shadow trick, use them as follows:
// a = width scaling (as mono and shad are drawn in the same way, copy mono.scaleX for a perfect fit
// b = 0, because we don't want to project the vertical axis of transformation to the horizontal
// c = horizontal skew
// d = height scaling * skew * making it a bit flat using the constant
// x = mono.x, ...
// y = mono.y since originally mono and shad look alike, only the Matrix makes shad render differently
var mtx:Matrix = new Matrix(mono.scaleX, 0, Math.cos(skew), mono.scaleY * Math.sin(skew) * MAX_SHADOW_HEIGHT_MULTIPLIER, mono.x, mono.y);
shad.transform.matrix = mtx;
}
Now all you got to know to utilize this in your case, is the following N factors:
Q1: from what angle you want to project the shadow?
A1: horizontal factor is the skew variable itself, while vertical angle is stored as constant here, called MAX_SHADOW_HEIGHT_MULTIPLIER
Q2: do you want to project shadow only "upwards", or freely?
A2: if "upwards" is fine, keep skew in the positive range, otherwise let it take negative values as well for a "downward" shadow
P.S.: if you render the internals of the objects that they don't snap to 0 y as a base point, you can make them seem float/sink, or offset both objects vertically with a predefined value, with the opposite sign.
You face 1 very simple problem, as you said:
'What I want to determine is the coordinates of the C & D points, thing that could be easy if I wasn't struggling to find the "Origin bis" coordinates.'
But these co-ordinates relate to each other, so without one (or another value such as an angle) you cannot have the other. If you are to try this in 3D you are simply allowing the 3D engine to define 'Origin bis' and do your calculating for C and D itself.
So regardless you will need an 'Original bis', another value relating to the redline or your Rect for which to calculate the placement of C and D.
I remember making stuff like this and sometimes it's better to just stick with simple, you either make an 'Original bis' defines by yourself (it can be either stationary or move with the player/background) and get C and D the way you got A and B only that you use a lower line than the red line, or as I would of done, once you have A and B, simple skew/rotate your projection from those points down a bit further, and you get something the same as an 'Original bis' that follows the player. This works fine at simulating 'feeling of something real' but sadly as has been said, it looking real depends on what you are portraying. We do not know what the areas above or below the red line are (sky/ground, ground/water) and whether 'Origin' and 'Origin bis' is your light source, vanishing point, etc.

Infinite horizontal scroll at constant speed in AS3 using TweenLite

I need to do an endless horizontal scroll of elements within a parent MovieClip.
No matter what ever method I try, an element of 'drift' occurs and eventually the elements start to overlap.
I've tried using relative recursive tweening for each element according
but this method seems prone to quite a bit of error after repeated starts and stops.
//CODE START
function doScroll():void {
TweenLite.to(this, .25, {x:"20", ease:Linear.easeNone,onUpdate:checkPos,onComplete:doScroll});
}
//CODE END
I've reverted to doing absolute tweens to a predefined position using a contant speed. This seems to be more accurate but still some 'drift' occurs.
//CODE START
//_dest is predefined
var speed:Number = 500;
var dist:Number = this.x - _dest;
var distAbs:Number = dist < 0 ? -dist : dist;
//kludge to get constant velocity by recalculating time every frame
_time = distAbs / speed;
TweenLite.to(this, _time, {x:_dest, ease:Linear.easeNone,onComplete:reset});
//CODE END
Thought this should be very simple.
Can anyone point me to any possible tutorials or make any suggestions?
Any help appreciated.
Solution/Discussion at http://forums.greensock.com/viewtopic.php?f=1&t=6800
(warning: this is gonna require a rather lengthy explanation...)
It's a logic problem in your code. In your onUpdate, you were running conditional logic such that if the x position is beyond 980, it kills the tween and moves x back to -980 and starts things over. You're doing that for each individual item, each of which begins at a different position. That initial position affects when it crosses that threshold, thus when they reposition, the offsets are different.
For example, let's say item1 starts at an x position of 0 and item2 starts at 490 and both start moving at 400 pixels per second and your frame rate is 60, thus they'll move 6.66666 pixels per frame. Item1 will take 147 frames to hit 980. However, item2 will take 74 frames (actually 73.5, but there's no such thing as a half-frame) to cross the 980 threshold, but when it does so it will be at an x position of 983.333333. At that point it jumps back to -980 due to your conditional logic, but notice that it traveled an EXTRA 3.333333 pixels. You intended Item1 and item2 to travel at the exact same velocities and they do during the tween, but your onUpdate logic is misaligning them on the reposition such that in the end, some are traveling more than others which affects their overall velocity.
Another issue has to do with the fact that Flash rounds x/y coordinates of DisplayObjects to the nearest 0.05. So when you do your manual reposition (wrap), small rounding errors creep in. For example, let's say TweenLite sets the exact x value to 980.799. Flash will actually round that to 980.75. Then when you reposition it like this.x -= 980 and then tween it, the value would have just lost almost 0.05 pixels on that round. Do that many times and it can add up to a half-pixel or whole pixel (or more). All your items are crossing the threshold at slightly different spots, thus the rounding errors aren't the same, thus you start seeing slight variances in the spacing. Again, this is NOT an issue with the tweening engine. You'll see that the engine itself sets the values correctly, but Flash rounds them internally when applied to DisplayObjects.
A solution was posted at http://forums.greensock.com/viewtopic.php?f=1&t=6800 that includes an FLA and support files.
As others have suggested, I'd recommend having a single chunk of code that manages ALL the items that you're aligning/scrolling. It would lay things out from a single reference point so that everything lines up perfectly every time. You could tween a getter/setter that applies the logic. I use that technique all the time and it works great. You can see a smaller-scale example in the code I attached in the above URL (the scrollX getter/setter in ItemBase.as)
If you will be tweening all background elements at the same rate indefinitely on a single dimension - why not use a Timer and bypass tweening libraries entirely?