# Marching Squares Visualized

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## How do I make an marching squares visualized?

A visualisation explaing a HTML5 Canvas implementation of the Marching Squares algorithm as it executes.. What is a marching squares visualized? How do you make a marching squares visualized? This script and codes were developed by Sakri Rosenstrom on 13 September 2022, Tuesday.

Marching Squares Visualized Previews

## Marching Squares Visualized - Script Codes HTML Codes

``````<!DOCTYPE html>
<html >
<body> <div id="canvasContainer"></div> <script src="js/index.js"></script>
</body>
</html>``````

## Marching Squares Visualized - Script Codes CSS Codes

``````html, body{	margin : 0px;	width : 100%;	height : 100%;	overflow: hidden;
}
#canvasContainer{ margin : 0px; width : 100%; height : 100%;
}``````

## Marching Squares Visualized - Script Codes JS Codes

``````/* * *Currently not working on Mac/FireFox and possibly other platforms *Sorry about this :( Will see if I can fix. * * @author Sakri Rosenstrom * A visualization explaining a Marching Squares algorithm as it executes * sample implementation here : https://codepen.io/sakri/full/vIKJp * http://www.sakri.net * https://twitter.com/sakri * http://www.devstate.net * Sources for this can be found at: * https://github.com/sakri/sakriNetCommonJS */
(function (window){ var Sakri = window.Sakri || {}; window.Sakri = window.Sakri || Sakri; Sakri.Geom = {}; //================================================== //=====================::POINT::==================== //================================================== Sakri.Geom.Point = function (x,y){ this.x = isNaN(x) ? 0 : x; this.y = isNaN(y) ? 0 : y; }; Sakri.Geom.Point.prototype.clone = function(){ return new Sakri.Geom.Point(this.x,this.y); }; Sakri.Geom.Point.prototype.update = function(x, y){ this.x = isNaN(x) ? this.x : x; this.y = isNaN(y) ? this.y : y; }; Sakri.Geom.Point.prototype.add = function(x, y){ this.x += isNaN(x) ? 0 : x; this.y += isNaN(y) ? 0 : y; }; Sakri.Geom.Point.prototype.equals = function(point){ return this.x==point.x && this.y==point.y; }; Sakri.Geom.Point.prototype.toString = function(){ return "{x:"+this.x+" , y:"+this.y+"}"; }; //================================================== //===================::RECTANGLE::================== //================================================== Sakri.Geom.Rectangle = function (x, y, width, height){ this.update(x, y, width, height); }; Sakri.Geom.Rectangle.prototype.update = function(x, y, width, height){ this.x = isNaN(x) ? 0 : x; this.y = isNaN(y) ? 0 : y; this.width = isNaN(width) ? 0 : width; this.height = isNaN(height) ? 0 : height; }; Sakri.Geom.Rectangle.prototype.getRight = function(){ return this.x + this.width; }; Sakri.Geom.Rectangle.prototype.getBottom = function(){ return this.y + this.height; }; Sakri.Geom.Rectangle.prototype.getCenter = function(){ return new Sakri.Geom.Point(this.getCenterX(), this.getCenterY()); }; Sakri.Geom.Rectangle.prototype.getCenterX = function(){ return this.x + this.width/2; }; Sakri.Geom.Rectangle.prototype.getCenterY=function(){ return this.y + this.height/2; };	Sakri.Geom.Rectangle.prototype.floor = function(){	this.x = Math.floor(this.x);	this.y = Math.floor(this.y);	this.width = Math.floor(this.width);	this.height = Math.floor(this.height);	}; Sakri.Geom.Rectangle.prototype.clone = function(){ return new Sakri.Geom.Rectangle(this.x, this.y, this.width, this.height); }; Sakri.Geom.Rectangle.prototype.toString = function(){ return "Rectangle{x:"+this.x+" , y:"+this.y+" , width:"+this.width+" , height:"+this.height+"}"; };
}(window));
/** * Created by sakri on 27-1-14. */
(function (window){ var Sakri = window.Sakri || {}; window.Sakri = window.Sakri || Sakri; Sakri.CanvasTextUtil = {}; //========================================================================================= //==============::CANVAS TEXT PROPERTIES::==================================== //======================================================== Sakri.CanvasTextProperties = function(fontWeight, fontStyle, fontSize, fontFace){ this.setFontWeight(fontWeight); this.setFontStyle(fontStyle); this.setFontSize(fontSize); this.fontFace = fontFace ? fontFace : "sans-serif"; }; Sakri.CanvasTextProperties.NORMAL = "normal"; Sakri.CanvasTextProperties.BOLD = "bold"; Sakri.CanvasTextProperties.BOLDER = "bolder"; Sakri.CanvasTextProperties.LIGHTER = "lighter"; Sakri.CanvasTextProperties.ITALIC = "italic"; Sakri.CanvasTextProperties.OBLIQUE = "oblique"; Sakri.CanvasTextProperties.prototype.setFontWeight = function(fontWeight){ switch (fontWeight){ case Sakri.CanvasTextProperties.NORMAL: case Sakri.CanvasTextProperties.BOLD: case Sakri.CanvasTextProperties.BOLDER: case Sakri.CanvasTextProperties.LIGHTER: this.fontWeight = fontWeight; break; default: this.fontWeight = Sakri.CanvasTextProperties.NORMAL; } }; Sakri.CanvasTextProperties.prototype.setFontStyle = function(fontStyle){ switch (fontStyle){ case Sakri.CanvasTextProperties.NORMAL: case Sakri.CanvasTextProperties.ITALIC: case Sakri.CanvasTextProperties.OBLIQUE: this.fontStyle = fontStyle; break; default: this.fontStyle = Sakri.CanvasTextProperties.NORMAL; } }; Sakri.CanvasTextProperties.prototype.setFontSize = function(fontSize){ if(fontSize && fontSize.indexOf && fontSize.indexOf("px")>-1){ var size = fontSize.split("px")[0]; fontProperites.fontSize = isNaN(size) ? 24 : size;//24 is just an arbitrary number return; } this.fontSize = isNaN(fontSize) ? 24 : fontSize;//24 is just an arbitrary number }; Sakri.CanvasTextProperties.prototype.getFontString = function(){ return this.fontWeight + " " + this.fontStyle + " " + this.fontSize + "px " + this.fontFace; };
}(window));
/** * Created by sakri on 27-1-14. */
(function (window){ var Sakri = window.Sakri || {}; window.Sakri = window.Sakri || Sakri; Sakri.BitmapUtil = {}; //TODO : rename "canvas" to "source", if it's an img, create a canvas and draw the img into it Sakri.BitmapUtil.getFirstNonTransparentPixelTopDown = function(canvas){ var context = canvas.getContext("2d"); var y, i, rowData; for(y=0; y<canvas.height; y++){ rowData = context.getImageData(0, y, canvas.width, 1).data; for(i=0; i<rowData.length; i+=4){ if(rowData[i+0] + rowData[i+1] + rowData[i+2] + rowData[i+3] > 0){ return new Sakri.Geom.Point(i/4, y); } } } return null; };
}(window));
/** * Created by @sakri on 28-1-14. * * Somewhat Naive implementation in that there are cases where the edge detection gets stuck in an eternal loop. * This is currently "handled" by a MAX_POINTS variable. * This implementation is "good enough" for most use cases though. * */
(function (window){ var Sakri = window.Sakri || {}; window.Sakri = window.Sakri || Sakri; Sakri.MarchingSquares = {}; //Update this when working with large shapes (large bitmaps) //the "edge detection loop" stops at this figure. This is in place in the event that an infinite loop somehow appears (Should never happen). Sakri.MarchingSquares.MAX_POINTS = 10000; //This is a lookup table of all possible 4 pixel grids, used to decide "scanning positions" during the edge detection process //Zeros represent transparent pixels, Ones represent a non transparent pixel Sakri.MarchingSquares.possibleGrids = { "0011":new Sakri.Geom.Point(1,0), "1011":new Sakri.Geom.Point(1,0), "0001":new Sakri.Geom.Point(1,0), "1001":new Sakri.Geom.Point(1,0), "0100":new Sakri.Geom.Point(0,-1), "0101":new Sakri.Geom.Point(0,-1), "0111":new Sakri.Geom.Point(0,-1), "0110":new Sakri.Geom.Point(0,-1), "1100":new Sakri.Geom.Point(-1,0), "1000":new Sakri.Geom.Point(-1,0), "1101":new Sakri.Geom.Point(-1,0), "1110":new Sakri.Geom.Point(0,1), "1010":new Sakri.Geom.Point(0,1), "0010":new Sakri.Geom.Point(0,1) }; /** * Apparently there were (are?) cases where duplicate points are registered along horizontal or vertical sets * of adjacent points. I haven't been able to reproduce this, but have left this option in place for now. */ Sakri.MarchingSquares.getUniquePoints = function(points){ console.log("MarchingSquares.getUniquePoints() points.length : ",points.length); var unique = {}; var uniquePoints = []; var pointString, p, i; for(i=0; i < points.length; i++){ p = points[i]; pointString = p.x+":"+p.y; if(unique[pointString] == null){ unique[pointString] = true; uniquePoints.push(p); } } console.log("MarchingSquares.getUniquePoints() uniquePoints.length : ",uniquePoints.length); return uniquePoints; }; //source can be a Canvas or an img element. See comment above getUniquePoints concerning the checkUnique flag Sakri.MarchingSquares.getBlobOutlinePoints = function(source, checkUnique){ //Create a copy with a one pixel blank "border" in case source image/canvas has pixels which touch the border //The edge scan operates with an offset of -1,-1 meaning the returned points are accurate var canvas = document.createElement("canvas"); canvas.width = source.width + 2; canvas.height = source.height + 2; var context = canvas.getContext("2d"); context.drawImage(source,1,1); if(checkUnique){ return Sakri.MarchingSquares.getUniquePoints(Sakri.MarchingSquares.scanOutlinePoints(canvas)); }else{ return Sakri.MarchingSquares.scanOutlinePoints(canvas); } }; //this should be private, should not be called directly Sakri.MarchingSquares.scanOutlinePoints = function(canvas){ var points = []; points[0] = Sakri.BitmapUtil.getFirstNonTransparentPixelTopDown(canvas); if(points[0] == null){ return points; } points[0].add(-1, -1);//in order for the lookup to work, we move the position up and back one var context = canvas.getContext("2d"); var currentPosition = points[0]; var gridString = Sakri.MarchingSquares.getGridStringFromPoint(context, currentPosition); var next, i; for(i=1; i<Sakri.MarchingSquares.MAX_POINTS; i++){ next = Sakri.MarchingSquares.getNextEdgePoint(currentPosition, gridString); if(next.equals(points[0])){ break; } points[i] = next; currentPosition = next; gridString = Sakri.MarchingSquares.getGridStringFromPoint(context, currentPosition); } //Failsafe when the marching squares get stuck in an eternal loop. See note at the top. if(i >= Sakri.MarchingSquares.MAX_POINTS){ console.log("MarchingSquares.scanOutlinePoints Sakri.MarchingSquares.MAX_POINTS reached"); return []; } return points; }; Sakri.MarchingSquares.getGridStringFromPoint = function(context, point){ var gridString = ""; var data = context.getImageData(point.x, point.y, 2, 2).data; for(i=0; i<16; i+=4){ gridString += (data[i+0] + data[i+1] + data[i+2] + data[i+3] > 0 ? "1" : "0"); } return gridString; }; Sakri.MarchingSquares.getNextEdgePoint = function(point, gridString){ var offsetPoint = Sakri.MarchingSquares.possibleGrids[gridString]; if(point==null){ throw new Error("MarchingSquares Error : gridString:"+gridString+" , not found in possibleGrids"); } return new Sakri.Geom.Point(point.x + offsetPoint.x, point.y + offsetPoint.y); };
}(window)); //======================== //general properties for demo set up //======================== var canvas; var context; var canvasContainer; var htmlBounds; var bounds; var minimumStageWidth = 250; var minimumStageHeight = 250; var resizeTimeoutId = -1; function init(){ canvas = document.createElement('canvas'); canvas.style.position = "absolute"; context = canvas.getContext("2d"); canvasContainer = document.getElementById("canvasContainer"); canvasContainer.appendChild(canvas); window.onresize = resizeHandler; commitResize(); } function getWidth( element ){return Math.max(element.scrollWidth,element.offsetWidth,element.clientWidth );} function getHeight( element ){return Math.max(element.scrollHeight,element.offsetHeight,element.clientHeight );} //avoid running resize scripts repeatedly if a browser window is being resized by dragging function resizeHandler(){ context.clearRect(0,0,bounds.width, bounds.height); clearTimeoutsAndIntervals(); clearTimeout (resizeTimeoutId); resizeTimeoutId = setTimeout(function(){commitResize();}, 300 ); } function commitResize(){ htmlBounds = new Sakri.Geom.Rectangle(0,0, getWidth(this.canvasContainer) , getHeight(canvasContainer)); if(htmlBounds.width>=800){ canvas.width = 800; canvas.style.left = htmlBounds.getCenterX() - 400+"px"; }else{ canvas.width = htmlBounds.width; canvas.style.left ="0px"; } if(htmlBounds.height>600){ canvas.height = 600; canvas.style.top = htmlBounds.getCenterY() - 300+"px"; }else{ canvas.height = htmlBounds.height; canvas.style.top ="0px"; } bounds = new Sakri.Geom.Rectangle(0,0, canvas.width, canvas.height); context.clearRect(0,0,bounds.width, bounds.height); if(bounds.width>bounds.height){ //landscape layout marchGridsBounds.x = bounds.getCenterX(); charactersBounds.x = marchGridsBounds.x - charactersBounds.width; charactersBounds.y = marchGridsBounds.y = bounds.getCenterY() - charactersBounds.height/2; }else{ //portrait layout charactersBounds.x = marchGridsBounds.x = bounds.getCenterX() - charactersBounds.width/2; marchGridsBounds.y = bounds.getCenterY() charactersBounds.y = marchGridsBounds.y - charactersBounds.height/2 } if(bounds.width<minimumStageWidth || bounds.height<minimumStageHeight){ stageTooSmallHandler(); return; } startDemo(); } function stageTooSmallHandler(){ var warning = "Sorry, bigger screen required :("; var props = new Sakri.CanvasTextProperties(null,null,24); context.font = props.getFontString(); context.fillStyle = "#000000"; context.fillText(warning, bounds.getCenterX() - context.measureText(warning).width/2, bounds.getCenterY()-12); } //======================== //Demo specific properties //======================== var marchingSquaresTimeOutId = -1; var fontProperties = new Sakri.CanvasTextProperties(Sakri.CanvasTextProperties.BOLD, null, 40); var fillStyle = "#0b0b2e"; var characters = "ABCDEFGHIJKLMNOPQRSTUVXYZ1234567890"; var currentCharacterIndex = 0; var currentCharacterOutline; var charactersBounds = new Sakri.Geom.Rectangle(0,0,250,250); var marchGridsBounds = new Sakri.Geom.Rectangle(0,0,250,250); var characterCanvas; var characterContext; var characterScaleFactor; var marchingPixelContext; var marchingPixelCanvas; var currentScanPosition; var optionGridRect = new Sakri.Geom.Rectangle(); var optionRect = new Sakri.Geom.Rectangle(); var bigBounds = new Sakri.Geom.Rectangle(); var outline; function clearTimeoutsAndIntervals(){ clearTimeout(marchingSquaresTimeOutId); } function startDemo(){ context.clearRect(0, 0, canvas.width, canvas.height); characterCanvas = document.createElement('canvas'); marchingPixelCanvas = document.createElement("canvas"); demoNextCharacter(); } function demoNextCharacter(){ context.clearRect(0,0,canvas.width, canvas.height); characterContext = characterCanvas.getContext("2d"); characterContext.clearRect(0,0,characterCanvas.width, characterCanvas.height); characterContext.font = fontProperties.getFontString(); characterContext.textBaseline = "top"; characterCanvas.width = characterContext.measureText(characters[currentCharacterIndex]).width; characterCanvas.height = fontProperties.fontSize; characterContext = characterCanvas.getContext("2d"); characterContext.fillStyle = "#AAAAAA"; characterContext.font = fontProperties.getFontString(); characterContext.textBaseline = "top"; characterContext.fillText(characters[currentCharacterIndex],0,0); renderCharacter(); renderAllOptions(); currentCharacterIndex++; currentCharacterIndex %= characters.length; marchingPixelCanvas.width = characterCanvas.width + 2; marchingPixelCanvas.height = characterCanvas.height + 2; marchingPixelContext = marchingPixelCanvas.getContext("2d"); marchingPixelContext.drawImage(characterCanvas,1,1); outline = []; outline[0] = Sakri.BitmapUtil.getFirstNonTransparentPixelTopDown(marchingPixelCanvas); outline[0].add(-1, -1);//in order for the lookup to work, we move the position up and back one currentScanPosition = outline[0].clone(); displayCurrentScanPosition(); } function displayCurrentScanPosition(){ renderCharacter(); context.fillStyle = "#FF0000"; var position; for(var i=0;i<outline.length;i++){ position = outline[i]; context.fillRect(charactersBounds.x+position.x, charactersBounds.y+position.y, 1, 1); context.fillRect(bigBounds.x+position.x*characterScaleFactor, bigBounds.y+position.y*characterScaleFactor, characterScaleFactor, characterScaleFactor ); } //render scan grid outline context.lineWidth = 1; context.strokeStyle = "#0000FF"; context.strokeRect(bigBounds.x+(currentScanPosition.x-1)*characterScaleFactor, bigBounds.y+(currentScanPosition.y-1)*characterScaleFactor, characterScaleFactor*2, characterScaleFactor*2); marchingSquaresTimeOutId = setTimeout(scanNextOutlinePoint, 500); renderAllOptions(); } function scanNextOutlinePoint(){ //console.log("scanNextOutlinePoint()"); var gridString = Sakri.MarchingSquares.getGridStringFromPoint(marchingPixelContext, currentScanPosition); var next = Sakri.MarchingSquares.getNextEdgePoint(currentScanPosition, gridString); if(next.equals(outline[0])){ demoNextCharacter(); return; } //render next renderAllOptions(gridString); currentScanPosition = next; outline.push(next); marchingSquaresTimeOutId = setTimeout(displayCurrentScanPosition, 500); } function renderCharacter(){ context.clearRect(charactersBounds.x, charactersBounds.y, charactersBounds.width, charactersBounds.height); var width = characterContext.measureText(characters[currentCharacterIndex]).width; var height = fontProperties.fontSize; characterScaleFactor = Math.floor(Math.min(charactersBounds.width / width, charactersBounds.height / height)); context.fillStyle = "#AAAAAA"; var data = characterContext.getImageData(0,0, width, height).data; var i, x, y; bigBounds.update(charactersBounds.x + width , charactersBounds.y, width*characterScaleFactor, height*characterScaleFactor); //render character for(i=0; i<data.length; i+=4){ if(data[i]+data[i+1]+data[i+2]+data[i+3] > 0){ x = (i/4)%width; y = Math.floor((i/4)/width); context.fillRect(charactersBounds.x + x, charactersBounds.y + y, 1, 1 ); context.fillRect(bigBounds.x+x*characterScaleFactor, bigBounds.y+y*characterScaleFactor, characterScaleFactor, characterScaleFactor ); } } //render graph lines context.fillStyle = "#FFFFFF"; for(i = characterScaleFactor; i < bigBounds.height; i+=characterScaleFactor){ context.fillRect(bigBounds.x, bigBounds.y + i, bigBounds.width, 1); } for(i = characterScaleFactor; i < bigBounds.width; i+=characterScaleFactor){ context.fillRect(bigBounds.x + i , bigBounds.y, 1, bigBounds.height); } } function renderAllOptions(currentOptionString){ context.clearRect(optionGridRect.x, optionGridRect.y, optionGridRect.width, optionGridRect.height); var margin = 4; var cols = 4; var optionSize = marchGridsBounds.width/cols; optionRect = new Sakri.Geom.Rectangle(0,0,optionSize-margin, optionSize-margin); optionGridRect.width = optionSize/2.5; optionGridRect.height = optionSize/2.5; var options = []; var i, option; for(option in Sakri.MarchingSquares.possibleGrids){ options.push({string:option, point:Sakri.MarchingSquares.possibleGrids[option]}); } for(var i=0; i<options.length; i++){ optionRect.x = marchGridsBounds.x + (i%cols) * optionSize; optionRect.y = marchGridsBounds.y + Math.floor(i/cols) * optionSize; optionRect.floor(); context.strokeStyle = currentOptionString==options[i].string ? "#FF0000" : "#AAAAAA"; context.strokeRect(optionRect.x, optionRect.y, optionRect.width, optionRect.height); renderOption(options[i], optionRect, currentOptionString==options[i].string); } } function renderOption(option, rect, highLight){ context.strokeStyle = highLight ? "#FF0000" : "#666666"; context.fillStyle = highLight ? "#FF0000" : "#333333"; optionGridRect.x = rect.getCenterX() - optionGridRect.width; optionGridRect.y = rect.getCenterY() - optionGridRect.height/2; context.strokeRect(optionGridRect.x, optionGridRect.y, optionGridRect.width, optionGridRect.height); //too lazy to write a loop for this, copy paste saves the day ;) if(option.string.charAt(0)=="1"){ context.fillRect(optionGridRect.x, optionGridRect.y, optionGridRect.width/2, optionGridRect.height/2 ); } if(option.string.charAt(1)=="1"){ context.fillRect(optionGridRect.x+optionGridRect.width/2, optionGridRect.y, optionGridRect.width/2, optionGridRect.height/2 ); } if(option.string.charAt(2)=="1"){ context.fillRect(optionGridRect.x, optionGridRect.y+optionGridRect.height/2, optionGridRect.width/2, optionGridRect.height/2 ); } if(option.string.charAt(3)=="1"){ context.fillRect(optionGridRect.x+optionGridRect.width/2, optionGridRect.y+optionGridRect.height/2, optionGridRect.width/2, optionGridRect.height/2 ); } optionGridRect.x = rect.getCenterX(); context.save(); context.lineWidth = 3; context.translate(optionGridRect.getCenterX()+optionGridRect.width/10, optionGridRect.getCenterY()); switch(option.point.x+""+option.point.y){ case "01": context.rotate(Math.PI/2); break; case "-10": context.rotate(Math.PI); break; case "0-1": context.rotate(Math.PI+Math.PI/2); break; } renderArrow(optionGridRect.width/2, optionGridRect.height/2); context.restore(); } function renderArrow(width,height){ //line context.beginPath(); context.moveTo(width/10, 0); context.lineTo(width-width/10, 0); context.stroke(); context.closePath(); //arrowhead context.beginPath(); context.moveTo(width/2, -height/2+height/10); context.lineTo(width-width/10, 0); context.lineTo(width/2, height/2-height/10); context.stroke(); context.closePath(); } var readyStateCheckInterval = setInterval( function() { if (document.readyState === "complete") { clearInterval(readyStateCheckInterval); init(); } }, 10);``````
 Developer Sakri Rosenstrom Username sakri Uploaded September 13, 2022 Rating 4 Size 7,074 Kb Views 26,312
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