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187 lines
8.2 KiB
TypeScript
187 lines
8.2 KiB
TypeScript
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/**
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* hsl - creates hsl color string from h, s and l values
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* @param h: number - hue
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* @param s: number - saturation
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* @param l: number - lightness
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*/
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function hsl(h: number, s: number, l: number): string {
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return `hsl(${h}, ${s}%, ${l}%)`
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}
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/**
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* render godrays
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* @param ctx: CanvasRenderingContext2D - where to draw
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* @param cx: number - x-axis center of the "sun"
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* @param cy: number - y-axis center of the "sun"
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* @param sunY: number - the position (height) of the "sun" in the sky
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* @param r: number [44] - the radius of the "sun"
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* @returns emissionStrength: number - emission intensity blends over the mountains
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*/
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function renderGodrays(ctx: CanvasRenderingContext2D, cx: number, cy: number, sunY: number, r = 44) {
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const w = ctx.canvas.width
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const h = ctx.canvas.height
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const emissionGradient = ctx.createRadialGradient(cx, cy, 0, cx, cy, r)
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ctx.fillStyle = emissionGradient
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// Now we addColorStops. This needs to be a dark gradient because our
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// godrays effect will basically overlay it on top of itself many many times,
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// so anything lighter will result in lots of white.
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// If you're not space-bound you can add another stop or two, maybe fade out to black,
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// but this actually looks good enough.
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// a black "gradient" means no emission, so we fade to black as transition to night or day
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let emissionStrength = 1.0
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if (sunY > -30) emissionStrength -= Math.max((30 + sunY) / 5, 0.0)
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else if (sunY < -60) emissionStrength += Math.min(1 + (60 + sunY) / 5, 0.0)
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emissionGradient.addColorStop(.1, hsl(30, 50, 3.1 * emissionStrength)) // pixels in radius 0 to 4.4 (44 * .1).
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emissionGradient.addColorStop(.2, hsl(12, 71, 1.4 * emissionStrength)) // pixels in radius 0 to 4.4 (44 * .1).
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// Now paint the gradient all over our godrays canvas.
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ctx.fillRect(0, 0, w, h)
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// And set the fillstyle to black, we'll use it to paint our occlusion (mountains).
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ctx.fillStyle = '#000'
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return emissionStrength
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}
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/**
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* calculate mountain height
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* Mountains are made by summing up sine waves with varying frequencies and amplitudes
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* The frequencies are prime, to avoid extra repetitions
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*/
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function calcMountainHeight(pos: number, roughness: number, frequencies = [1721, 947, 547, 233, 73, 31, 7]) {
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return frequencies.reduce((height, freq) => height * roughness - Math.cos(freq * pos), 0)
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}
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/**
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* render mountains
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* @param ctx: CanvasRenderingContext2D - where to draw
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* @param grCtx: CanvasRenderingContext2D - for drawing mountain shadows on the godray canvas
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* @param frame: number - current frame (position on the x axis)
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* @param sunY: number - position (height) of the "sun" in the sky
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* @param layers: number - amount of mountain layers for parallax effect
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* @param emissionStrength: number - intensity of the godrays
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*/
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function renderMountains(ctx: CanvasRenderingContext2D, grCtx: CanvasRenderingContext2D, frame: number, sunY: number, layers: number, emissionStrength: number) {
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const w = ctx.canvas.width
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const h = ctx.canvas.height
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const grDiv = w / grCtx.canvas.width
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for (let i = 0; i < layers; i++) {
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// Set the main canvas fillStyle to a shade of green-brown with variable lightness
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// depending on sunY and depth
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ctx.fillStyle = sunY > -60
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? hsl(5, 23, 33*emissionStrength - i*6*emissionStrength)
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: hsl(220 - i*40, 23, 33-i*6)
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for (let x = w; x--;) {
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// Ok, I don't really remember the details here, basically the (frame+frame*i*i) makes the
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// near mountains move faster than the far ones. We divide by large numbers because our
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// mountains repeat at position 1/7*Math.PI*2 or something like that...
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const pos = (frame * 2 * i**2) / 1000 + x / 2000
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// Make further mountains more jagged, adds a bit of realism and also makes the godrays
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// look nicer.
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const roughness = i / 19 - .5
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// 128 is the middle, i * 25 moves the nearer mountains lower on the screen.
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let y = 128 + i * 25 + calcMountainHeight(pos, roughness) * 45
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// Paint a 1px-wide rectangle from the mountain's top to below the bottom of the canvas.
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ctx.fillRect(x, y, 1, h)
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// Paint the same thing in black on the godrays emission canvas, which is 1/4 the size,
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// and move it one pixel down (otherwise there can be a tiny underlit space between the
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// mountains and the sky).
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grCtx.fillRect(x/grDiv, y/grDiv+1, 1, h)
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}
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}
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}
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/**
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* render sky
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* @param ctx: CanvasRenderingContext2D - where to draw
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* @param sunY: number - the position (height) of the "sun" in the sky
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*/
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function renderSky(ctx: CanvasRenderingContext2D, sunY: number) {
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const w = ctx.canvas.width
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const h = ctx.canvas.height
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const skyGradient = ctx.createLinearGradient(0, 0, 0, h)
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const skyHue = 360 + sunY // hue from blue to red, depending on the suns position
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const skySaturation = 100 + sunY // less saturation at day so that the red fades away
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const skyLightness = Math.min(sunY * -1 - 10, 55) // darker at night
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const skyHSLTop = `hsl(220, 70%, ${skyLightness}%)`
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const skyHSLBottom = `hsl(${skyHue}, ${skySaturation}%, ${skyLightness}%)`
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skyGradient.addColorStop(0, skyHSLTop)
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skyGradient.addColorStop(.7, skyHSLBottom)
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ctx.fillStyle = skyGradient
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ctx.fillRect(0, 0, w, h)
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}
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/**
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* useBackground
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* @param canvasEl: HTMLCanvasElement - the canvas to draw the background on.
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* @param w: number - the (pixel) width of the canvas. The element itself can have a different width.
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* @param h: number - the (pixel) height of the canvas. The element itself can have a different height.
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* @param rayQuality: number [8] - The quality of the sunrays (divides the resolution, so higher value means lower quality)
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* @param mountainLayers: number [4] - How many layers of mountains are used for parallax effect?
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*/
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export default function useBackground (canvasEl: HTMLCanvasElement, w: number, h: number, rayQuality = 8, mountainLayers = 4) {
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canvasEl.width = w
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canvasEl.height = h
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const grW = w / rayQuality
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const grH = h / rayQuality
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const ctx = canvasEl.getContext('2d')
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if (ctx === null) return // like, how old is your browser?
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const grCanvasEl = document.createElement('canvas')
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const grCtx = grCanvasEl.getContext('2d')
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if (grCtx === null) return // like, how old is your browser?
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grCanvasEl.width = grW
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grCanvasEl.height = grH
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const sunCenterX = grCanvasEl.width / 2
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const sunCenterY = grCanvasEl.height / 2
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/**
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* draw one frame of the background
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* @param frame: number - the position on the x axis, to calculate the paralax background
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* @param sunY: number - the position (height) of the sun in the sky
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*/
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return function drawFrame (frame: number, sunY: number) {
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console.log('drawing frame', frame, sunY)
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const emissionStrength = renderGodrays(grCtx, sunCenterX, sunCenterY, sunY)
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renderSky(ctx, sunY)
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renderMountains(ctx, grCtx, frame, sunY, mountainLayers, emissionStrength)
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// The godrays are generated by adding up RGB values, gCt is the bane of all js golfers -
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// globalCompositeOperation. Set it to 'lighter' on both canvases.
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ctx.globalCompositeOperation = grCtx.globalCompositeOperation = 'lighter'
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// NOW - let's light this m**f** up! We'll make several passes over our emission canvas,
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// each time adding an enlarged copy of it to itself so at the first pass we get 2 copies, then 4,
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// then 8, then 16 etc... We square our scale factor at each iteration.
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for (let scaleFactor = 1.07; scaleFactor < 5; scaleFactor *= scaleFactor) {
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// The x, y, width and height arguments for drawImage keep the light source in the same
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// spot on the enlarged copy. It basically boils down to multiplying a 2D matrix by itself.
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// There's probably a better way to do this, but I couldn't figure it out.
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// For reference, here's an AS3 version (where BitmapData:draw takes a matrix argument):
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// https://github.com/yonatan/volumetrics/blob/d3849027213e9499742cc4dfd2838c6032f4d9d3/src/org/zozuar/volumetrics/EffectContainer.as#L208-L209
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grCtx.drawImage(
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grCanvasEl,
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(grW - grW * scaleFactor) / 2,
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(grH - grH * scaleFactor) / 2 - sunY * scaleFactor + sunY,
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grW * scaleFactor,
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grH * scaleFactor
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)
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}
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// Draw godrays to output canvas (whose globalCompositeOperation is already set to 'lighter').
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ctx.drawImage(grCanvasEl, 0, 0, w, h);
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}
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}
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