js canvases stacking order - javascript

I apologise if this is not the right place for beginner's question
This is my first search for help in stack overflow and I am only beginning with js.
Disclaimer: I am trying to explore Physics examples from a book and concentrating only in learning about the canvas. I know practically NOTHING about HTML/CSS; just the bare essentials to play in the canvas (so far, I have already balls jumping & collision testing etc).
I have drawn three partially overlapping squares of different colors (red blue black) in three corresponding canvas(es) named as "layer1" "layer2" "layer3" in this order and I can see them piled in their expected stacking order: black on top of blue on top of red.
I have set up a keydown event listener and am trying to use switch to change the stacking order, but have been unsuccessful.
function moveLayers(evt) {
switch(evt.keyCode) {
case 37: // up arrow
// what code should go here to change the order of layer1 and layer3
break;
}
}
Yes I found it has to do with z-indez, but don't know exactly the syntax needed
Thanks for replying with the specific line of code (I suspect it is just a one liner) or nudging me in the right direction.

I knew it should just one line!
Found out at Style zIndex Property at
http://www.w3schools.com/jsref/prop_style_zindex.asp
solution:
to change layer 3 to layer 1, just write:
document.getElementById("layer3").style.zIndex = "1";

Related

Sprite not properly displaying

I'm using Code.org's game lab to make Tetris, and I have this sprite. https://ibb.co/zsT4LN6
You see the gray spots? They're like an empty background, but whenever a sprite touches the empty background, it stops moving. I want it to ignore the empty space. Is there a way to remove that or a block code to detect if a sprite touches a color
Sounds like your hitbox is different then you want.
Option 1: graphical editing (design view)
In GameLab you can change this within the tab "Animation".
On the far right I see following elements:
Resize as the top option (purple icon)
Crop the Sprite as the bottom option (grey tiles)
Option 2: writing code (source view)
There are two approaches (commands on sprite) you'll want to try:
Use sprite.debug to set the sprite's debug state to true. Then next time you run your code it will display a neon-green hitbox around the sprite.
You can change that hitbox through code using sprite.setCollider().
Both commands are demonstrated in the following snipped:
sprite.debug = true;
sprite.setCollider("rectangle", 0, 0, 20, 80, -45);

Drag and mouseover in snap.svg

I'm relatively new to javascript, and am learning about drag and drop using snap.svg. My problem is in the drop. I can't tell if the dragged element is over the drop target. In this code, I want to drag the circle over the square, and thought I could use mouseover. My (distilled) example may also be a simpler version of this post.
var paper = Snap(300, 300);
var square = paper.rect(100, 100, 40, 40).attr({fill:"blue"});
var circle = paper.circle(50, 50, 20).attr({fill:"red"});
circle.drag();
square.mouseover(
function() {
console.log("Over the square");
}
);
As written, the mouseover will fire when you move the pointer over the blue square, but not when you drag the red circle over the blue square. If you reverse the creation of the square and circle, the mouseover fires either way, but of course the circle is behind the square.
Evidently the event gets caught in the view hierarchy (or something) and doesn't propagate. There must be an easy way around this. Any help?
(And if the best answer is, "use jQuery," fine, but I'd love to learn how to make this work directly, since snap.svg makes dragging so easy.)
Addition: The direction I'm hoping for: the snap.svg documentation for Element.drag() says, in part, "When Element is dragged over another element, drag.over.<id> fires as well." A fine, event-based direction, which would let me (for example) highlight the drop target without a lot of fuss.
But I haven't figured out how to listen for that event! Any help or advice?
Only quick way without collision or element detection from points that I can think of, is to place an almost invisible clone in front of the object, later in the DOM that you can't really see, eg ...
paper.append( square.clone().attr({ opacity: 0.000001 }) )
jsfiddle
Depends how complex your svgs are going to be as to whether this would work I guess, you also have a slight issue if you drop the element over it, your redrag start won't get picked up, so you would need to code around that as well. I think some testing is probably going to be the most bug free solution (there are a few solutions on S.O for getElementFromPoint or hit detection type solutions).
jsfiddle workaround for point above

Circular canvas corners clickable in Chrome

I have two canvases. I have made them circular using border-radius. The 2nd is positioned inside the first one (using absolute position).
I have click events on both circles. If you click on inside canvas, the color at the point of the click is loaded in the outside canvas with opacity varying from white to the picked color and finally to black. If you click on outer canvas the exact color value at that point is loaded in the text-box at the bottom
I am unable to click in red zones (as shown in figure below) of the outer canvas when using chrome. I tried z-idex, arcs but nothing is helping me. But In Firefox everything is working fine.
Note: You can drag the picker object in the outer circle. But if you leave it in red zones, you would not be able to click it again in Chrome. Clicking in green zone will get you its control again
Code in this JSFiddle
Edit
I excluded all irrelevant code to make it easy. Now there is only a container having two canvas.
Filled simply with two distinct colors. Open following fiddle link in both chrome and firefox. Click on both cirles in different zones and see difference in chrome and firefox. I want them to behave in chrome as they do in firefox
Note I will ultimately draw an image in inner canvas.
Updated Fiddle Link
-
Your problem is because canvases currently are always rectangular, even if they don't look rectangular. Border radius makes the edges except the circle transparent, but it still doesn't stop events in Chrome on the corner areas. This is why you cannot click the bottom circle in those areas
I even tried putting it inside of a container that had a border-radius instead but the click event still goes through
With that being said, you have two options. You could either change your code to only use one canvas with the same type of layout, just drawing the background circle before the other each time. Essentially you'd draw a circle, draw your black to color to white gradient, use the xor operation to combine the two into one circle, then do the same with the rainbox gradient. You must draw the background circle first because canvas paints over the old layers every time
or
You could use javascript to only detect clicks in the circular area which takes just a little bit of math (: This solution is featured in edit below
In the future, CSS Shapes may allow canvases to be non-rectangular elements to be used, I'm actually not sure, but we don't have that capability yet at least
Edit
Alright, so after going through your code a bit it seems there are some things I should cover before I offer a solution
Setup all your finite variables outside of the functions that run every time. This means you don't put them (like radiuses, offsets, etc.) in the click function or something that runs often since they don't change
Your "radius"es are actually "diameter"s. The format of .rect goes .rect(x, y, width (diameter of circle), height (diameter of circle))
Almost always when overlaying canvases like you are you want to make them equal dimensions and starting position to prevent calculation error. In the end it makes it easier, doing all relative positioning with javascript instead of mixing it with CSS. In this case, however, since you're using border-radius instead of arc to make a circle, keep it like it is but position it using javascript ....
jQuery isn't needed for something this simple. If you're worried about any load speed I'd recommend doing it in vanilla javascript, essentially just changing the .click() functions into .onclick functions, but I left jQuery for now
You can declare multiple variables in a row without declaring var each time by using the following format:
var name1 = value1,
name2 = value2;
Variables with the same value you can declare like so:
var name1 = name2 = sameValue;
When children have position:absolute and you want it to be positioned relative to the parent, the parent can have position:relative, position:fixed, or position:absolute. I would think you'd want position:relative in this case
When you don't declare var for a variable it becomes global (unlessed chained with a comma like above). For more on that read this question
Now, onto the solution.
After talking with a friend I realized I could sort do the math calculation a lot easier than I originally thought. We can just calculate the center of the circles and use their radiuses and some if statements to make sure the clicks are in the bounds.
Here's the demo
After everything is set up correctly, you can use the following to detect whether or not it's in the bounds of each
function clickHandler(e, r) {
var ex = e.pageX,
ey = e.pageY,
// Distance from click to center
l = Math.sqrt(Math.pow(cx - ex, 2) + Math.pow(cy - ey, 2));
if(l > r) { // If the distance is greater than the radius
if(r === LARGE_RADIUS) { // Outside of the large
// Do nothing
} else { // The corner area you were having a problem with
clickHandler(e, LARGE_RADIUS);
}
} else {
if(r === LARGE_RADIUS) { // Inside the large cirle
alert('Outer canvas clicked x:' + ex + ',y:' + ey);
} else { // Inside the small circle
alert('Inner canvas clicked x:' + ex + ',y:' + ey);
}
}
}
// Just call the function with the appropriate radius on click
$(img_canvas).click(function(e) { clickHandler(e, SMALL_RADIUS); });
$(wheel_canvas).click(function(e) { clickHandler(e, LARGE_RADIUS); });
Hopefully the comments above and code make enough sense, I tried to clean it up as best as I could. If you have any questions don't hesitate to ask!

KineticJS: Draw Arrow between two shapes

So, I want to create a finite state machine-visualizer/editor with the help of kineticjs and i'm stumbling with the following scenario:
I have two "nodes", let's say circle-objects (grouped with a label) which are draggable on my stage. Now I wan't to click on one circle, hold the mouse and move it and add a connection (an arrow, for simplicities sake) between the two shapes.
So it would be great to have any hints on how to accomplish this for I haven't found a solution yet.
To specify it: The nodes themselves should stay draggable. My thought was: Add a black circle and a white circle with a slightly smaller radius, group them. then on dragstart white circle -> drag node, on dragstart black circle -> draw arrow.
The Problem is how to draw an arrow starting from one shape and following the mouse to it's target (which can be another nodegroup => connection to this group or a blank point of the stage => an overlay opens which lets the user choose another node to draw or cancel the drawing).
I hope this is somewhat clear to understand. For more information please feel free to ask me.
Best regards,
Dominik
p.s.: The behaviour seems to be exactly like the behaviour lucidchart (dot com) uses when creating diagrams, so maybe you understand what I want to achieve better looking at their demo here: https://www.lucidchart.com/demo .
First off, for simplicity's sake here is a fiddle on how to draw a basic Line with your mouse and KineticJS: http://jsfiddle.net/projeqht/fF3hh/
Let's say you already have two circles on the stage, and you need to draw a line to connect them.
We can use e.targetNode to select the nodes on each event (mousedown, mouseup), for example:
layer.on("mousedown", function (e) {
var nodeDown = e.targetNode;
}
layer.on("mouseup", function (e) {
var nodeUp = e.targetNode;
}
We need to check if the parent of nodeDown is a Kinetic.Group or something else.
If the target node nodeDown has a Kinetic.Group for a parent, we can use this Group to store the new line, and the 2nd target node nodeUp.
If the target node nodeUp does not have a Kinetic.Group for a parent, we need to see if nodeUp has a Group for a parent. If nodeUp has a Kinetic.Group for a parent, then we can use that Group to store the new line, and the first target node nodeDown.
If neither nodeDown or nodeUp have a group for a parent, then we will need to create a new group for them and add all 3 shapes (2 circles and a line) to that new group.
Use this tutorial to learn how to move shapes from 1 group to another: http://www.html5canvastutorials.com/kineticjs/html5-canvas-move-shape-to-another-container-with-kineticjs/
Also, if you move a shape from one group to another, you may want to remove() or destroy() the extra group if it is no longer needed.
While drawing a Line, you will have to disable dragging the shapes, so that you can drag and draw with a mouse. You can do that by doing something similar to this:
function stopDrag() {
for (var i=0; i<layer.children.length; i++) {
layer.children[i].setDraggable(false);
}
}
function startDrag() {
for (var i=0; i<layer.children.length; i++) {
layer.children[i].setDraggable(true);
}
}
This will make all the children of layer draggable and undraggable, but you might want to limit that by being more specific than select layer.children. A nice trick I liked to use here was to name all groups that were draggable as "draggable_shapes" and then use var draggableArray = stage.get('.draggable_shapes') to select all the groups that are allowed to be dragged, then you could loop through that array and setDraggable().
Another point to note is that the X and Y coordinates of the Line will be a bit tricky to calculate, depending on if it has a Group as a parent or a Layer. If the Line is grouped, line's coordinates will be relative to the Group position, or else the Line's coordinates will be relative to the Stage (top left corner).
This will get you started on connecting a line with two different circles. It's up to you to do the coordinate logic if you want the lines to only connect on the outer rim of the circles.
Maybe you might want to add a transparent rectangle (attribute opacity: 0) behind each circle, so that on mousedown with the rectangle, you will call drawLine() to start drawing a line. Or else if the user clicks the circle, it will drag the group. At least that has similar functionality to the lucid charts application.
Custom Hit Function (http://www.html5canvastutorials.com/kineticjs/html5-canvas-kineticjs-custom-hit-function-tutorial/) would probably be a cleaner way to do this but I'm not 100% on using Custom Hit Functions, someone else might know better.
Let me know if you need further help. Good luck!

Making Javascript TileEngine Scrollable in Canvas

The basis for the code is from John E. Graham's blog http://johnegraham2.com/blog/2010/09/25/project-javascript-2d-tile-engine-with-html5-canvas-part-4-using-zones-for-further-optimization/
It works perfectly for drawing a screen's worth of tiles, but I cannot for the life of me figure out how to adjust it 1 row/column at a time based on pressing up, down, left, or right keys.
Here is an example with the transparency to help visualize the zones http://simplehotkey.com/Javascript/canvas.html (loading positions of 1,188 tiles but only draws a couple hundred to fill the screen) I had it loading an array with 70,000 entries and it was still quick because it's only drawing whats on the screen, but cannot figure out how to slide everything based on input...
I've come up with a couple ideas and am not sure what's the best way.
One screen worth of tiles is shown here:
tilesArray = [
0,0,0,0,0,0,0,1,2,9,6,0,0,7,0,0,1,0,
0,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,0,
0,9,9,9,9,9,9,9,9,9,9,9,9,9,9,0,9,0,
0,9,9,9,9,9,9,9,9,9,9,9,9,9,9,0,9,0,
0,9,9,9,9,9,9,0,7,2,0,0,0,0,0,1,2,0,
0,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,0,
0,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,0,
0,9,0,7,2,9,9,9,9,9,9,9,9,9,9,9,9,0,
0,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,0,
0,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,0,
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
];
Where 0 is a wall tile (around perimeter), 9 a floor tile, 7 a door and a couple other random tiles.
That is exactly what is loaded to the screen, but I cannot figure out how to shift everything 1 tile in either direction based on input, up, down, left, right.
The one idea I'm leaning towards now, is just to use that array above as the basis for rendering, and somehow feeding the new values into it based on keyboard input, from another array. Maybe slicing from another, much larger array (holding all the tiles for the entire level) and using that slice to populate the array that's actually rendered???
That's replacing every tile every frame though...
for getting player input I was using:
//Key listener
document.onkeydown = function(e){
e = e?e:window.event;
console.log(e.keyCode + "Down");
switch (e.keyCode){
case 38:
//UP KEY
Game.inputReaction('up');
//Game.moveDir('up');
break;
case 40:
//DOWN KEY
//Game.inputReaction(40);
//Game.moveDir('down');
break;
case 37:
//Left Key
//Game.inputReaction(37);
break;
}
}
The other alternative is to try to adjust the tiles already on the screen and add new tiles but this engine isn't using global variables so I'm not sure how to affect the tile engine programatically based on input....like I can add another method (inputReaction(num)) and trigger some actions from my keyboard input (console.log()) but I can't access the other methods actually drawing the tiles. Or maybe I have to make a copy of the object, change it and return it? but it's pretty complex.
I think it might be easier to adjust the array values that are being fed into the "engine" (array above) rather than changing around how the engine is calculating what's being drawn. Can you confirm this?
Add a camera abstraction that you can move around on the map, then shift the drawing positions according to the camera position. When the camera moves south 10px, all tiles move north 10px, same with east and west. Since you only draw the tiles that are visible, there won't be much of a performance loss.
The renderer looks at the camera to figure out what needs to be drawn and you can expose the camera object to the outside to manipulate it. That way you only need to change the camera position to change what is shown on the screen.
I did this in a proof of concept tiling engine a year ago and I was able to smoothly scroll and scale huge tilemaps.
If you start changing the array itself, your performance will suffer and you won't be able to scroll smoothly since you can only go in steps of one tile and not one pixel.

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