Changing the FPS cap and manipulating pixels causes an permanent FPS drop whenever the cursor clicks/hovers on the page

[motis1]

Most appropriate sub-area of p5.js?

• Accessibility
• Color
• Core/Environment/Rendering
• Data
• DOM
• Events
• Image
• IO
• Math
• Typography
• Utilities
• WebGL
• Build Process
• Unit Testing
• Internalization
• Friendly Errors
• Other (specify if possible)

p5.js version

1.7.0

Web browser and version

Google Chrome: 117.0.5938.92 (Official Build) (64-bit) (cohort: Stable)

Operating System

Windows 10 Pro: 10.0.19045 Build 19045

Steps to reproduce this

Details

Changing the FPS cap and manipulating pixels causes a permanent drop in performance whenever the cursor clicks/hovers on the page.

It also appears that the FPS drop incurred by hovering over the page can only happen for a short period of time after the page has just loaded but clicking seems to work whenever during the lifetime of the page.

P.S. I accidentally created an empty issue whilst trying to create this one. If it could be deleted by someone who can it would be greatly appreciated.

Steps:

1. Run the code snippet attached to this issue
2. Hover/Click on the page/canvas and notice the drop in FPS.
3. If you do not observe a drop in FPS, consider adjusting the SIZE constant so that there is enough load to make the baseline FPS below that of your monitors refresh rate.

Snippet:

const SIZE = 600;
const FRAME_RATE = 999;

function setup() {
    createCanvas(SIZE, SIZE);
    frameRate(FRAME_RATE);
}

function draw() {
    background(0);

    for (let y = 0; y < SIZE; y++) {
        for (let x = 0; x < SIZE; x++) {
            set(x, y, 0);
        }
    }

    updatePixels();

    fill(255);
    text(Math.round(frameRate()), 50, 50);
}

[davepagurek]

Do you see a similar slowdown when using loadPixels(), updating the pixels[] array, then calling setPixels()? It's known that calling set() to update a grid of pixels will be slow, as it tries to update the canvas after each call rather than doing it all at once.

[motis1]

Yes, it is possible to observe this problem using the pixels[] array along with loadPixels() and updatePixels() instead of the set() method.

Using the following code, it is possible to observe this problem using a simple graph using both the pixels[] and set().
For reasons unknown to me, this bug is not reproducible inside the p5.js editor.
For the best results run the JavaScript inside of a basic HTML page with p5.js included using a CDN.

const SIZE = 800;
const FRAME_RATE = 180;

let graphTicks = [];

function drawGraph() {
    noFill();
    stroke(255);
    beginShape();

    for (let i = 0; i < graphTicks.length; i++) {
        let x = (graphTicks[i].timestamp / frameCount) * SIZE;
        let y = SIZE - ((graphTicks[i].frameRate / FRAME_RATE) * SIZE);

        curveVertex(x, y);
    }

    endShape();
}

function useSetFunc() {
    for (let y = 0; y < SIZE; y++) {
        for (let x = 0; x < SIZE; x++) {
            set(x, y, 0);
        }
    }

    updatePixels();
}

function usePixelsArray() {
    loadPixels();

    for (let y = 0; y < SIZE; y++) {
        for (let x = 0; x < SIZE; x++) {
            let d = pixelDensity();
            for (let i = 0; i < d; i++) {
                for (let j = 0; j < d; j++) {
                    // loop over
                    index = 4 * ((y * d + j) * width * d + (x * d + i));
                    pixels[index] = 0;
                    pixels[index + 1] = 0;
                    pixels[index + 2] = 0;
                    pixels[index + 3] = 255;
                }
            }
        }
    }

    updatePixels();
}

function setup() {
    createCanvas(SIZE, SIZE);
    frameRate(FRAME_RATE);
}

function draw() {
    graphTicks.push({
        timestamp: frameCount,
        frameRate: frameRate()
    });

    background(0);

    // Uncomment one of the two functions
    // useSetFunc();
    usePixelsArray();

    drawGraph();

    fill(255);
    noStroke();
    text(Math.round(frameRate()), 50, 50);
}

[Vishal2002]

Is this issue still open for contribution?

[rayyan21d]

I'm interested in contributing to this issue @motis1
Are there any helpful docs that would help me better understand this?

[davepagurek]

Thanks @Vishal2002 for doing some profiling! It seems like there's not a new function being called after a click, but rather, the set() function just gets slower. Some additional notes from some more testing on my end:

• The slowdown is less apparent on 1.9.0 than 1.7.0, but still present
• I don't notice a slowdown in Firefox, just Chrome
• I can personally reproduce this within the p5 editor

@rayyan21d the way we've been testing so far is with the browser profiler, where each draw call takes longer after clicking compared to before:

I wonder if this is a known thing in Chrome? Maybe some of you can help look up any existing Chrome/Chromium bug reports that sound similar?

Another way to investigate further: is it also faster on 1.9.0 compared to 1.7.0 for you? If so, you can try using git bisect to find a commit between then and now where the slowness gets better, just so we can get a sense of what affects it. It doesn't look like any significant changes happened between those versions to the set() or updatePixels() methods, just some indentation fixes.