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POMultiple light sources on canvas
 

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    <p>I want to place a number of light sources on a background for a game I'm making, which works great with one light source as shown below:</p> <p><img src="https://i.stack.imgur.com/ymRsf.png" alt="enter image description here"></p> <p>This is achieved by placing a .png image above everything else that becomes more transperant towards the center, like this:</p> <p><img src="https://i.stack.imgur.com/kNJcv.png" alt="enter image description here"></p> <p>Works great for one light source, but I need another approach where I can add more and move the light sources around.</p> <p><img src="https://i.stack.imgur.com/CIWiS.png" alt="enter image description here"></p> <p>I have considered drawing a similar "shadow layer" pixel by pixel for each frame, and calculate the transparency depending of the distance to each light source. However, that would probably be very slow and I'm sure there are way better solutions to this problem.</p> <p>The images are just examples and each frame will have considerably more content to move around and update using requestAnimationFrame.</p> <p>Is there a light weight and simple way to achieve this? Thanks in advance!</p> <p><strong>Edit</strong></p> <p>With the help of ViliusL, I came up with this masking solution:</p> <p><a href="http://jsfiddle.net/CuC5w/1/" rel="nofollow noreferrer">http://jsfiddle.net/CuC5w/1/</a></p> <pre><code>// Create canvas var canvas = document.createElement('canvas'); var ctx = canvas.getContext('2d'); canvas.width = 300; canvas.height = 300; document.body.appendChild(canvas); // Draw background var img=document.getElementById("cat"); ctx.drawImage(img,0,0); // Create shadow canvas var shadowCanvas = document.createElement('canvas'); var shadowCtx = shadowCanvas.getContext('2d'); shadowCanvas.width = canvas.width; shadowCanvas.height = canvas.height; document.body.appendChild(shadowCanvas); // Make it black shadowCtx.fillStyle= '#000'; shadowCtx.fillRect(0,0,canvas.width,canvas.height); // Turn canvas into mask shadowCtx.globalCompositeOperation = "destination-out"; // RadialGradient as light source #1 gradient = shadowCtx.createRadialGradient(80, 150, 0, 80, 150, 50); gradient.addColorStop(0, "rgba(255, 255, 255, 1.0)"); gradient.addColorStop(1, "rgba(255, 255, 255, .1)"); shadowCtx.fillStyle = gradient; shadowCtx.fillRect(0, 0, canvas.width, canvas.height); // RadialGradient as light source #2 gradient = shadowCtx.createRadialGradient(220, 150, 0, 220, 150, 50); gradient.addColorStop(0, "rgba(255, 255, 255, 1.0)"); gradient.addColorStop(1, "rgba(255, 255, 255, .1)"); shadowCtx.fillStyle = gradient; shadowCtx.fillRect(0, 0, canvas.width, canvas.height); </code></pre>
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    1. COWell i have another suggestion if you're interested : see here to watch the result (especially the right candle) http://jsfiddle.net/gamealchemist/ABfVj/
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    2. COGreat solution! I'll give them both a try in the actual game to see which works best.
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    3. COAbout your 1 px issue : Be aware that, even if imho it is a mistake, the stroke of a geometry is centered, it's not topped by the geometry dimensions. So when you do ctx.arc(.,., r ,...) + ctx.stroke(); you probably mean ctx.arc(.,., r - ctx.lineWidth/2 , ...) + ctx.stroke();
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