2024 06 06 troubleshooting an image width issue and implementing a guard solution - bizkite-co/handterm GitHub Wiki

original file name: Codeium Chat - KkUgJq72ZADHARAqFlmkVymeJZMKEkrO.md summary: The user faced an issue where an image was coming in with a width of 0 in their code block, potentially leading to an infinite loop. They sought guidance on creating a guard against this scenario. The assistant provided a solution by suggesting to check if the image width is 0 before proceeding with the drawing logic in the drawParallaxLayer function. They recommended modifying the function to include an if statement to handle cases where the image width is 0, and to ensure the width is at least 1 to prevent division by zero when calculating the number of images to draw. date: 2024-06-06T08:04

Codeium Chat Conversation

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User at 8:04 am, Jun 6, 2024

For some reason, the image is coming in with a width of 0 in this code block.

The image should not be zero, but more distressingly, if it is zero, we end up with an infinite loop.

How can we create a better guard against that?

drawParallaxLayer(context: CanvasRenderingContext2D, image: HTMLImageElement, scale: number, movementRate: number) {
  const layerHeight = this.props.canvasHeight * scale;
  const scaledWidth = image.width * scale;

  // Calculate how many times the image should be drawn to cover the canvas width
  const numImages = Math.ceil(this.props.canvasWidth / scaledWidth) + 1;

  // Calculate the offset for when the image scrolls
  const offsetX = -(this.state.backgroundOffsetX * movementRate) % scaledWidth;

  context.save(); // Save the current context state
  // context.globalAlpha = scale === 0.8 ? 0.5 : 0.6; // Adjust transparency for effect if desired

  // Draw the scaled image multiple times to cover the canvas width
  for (let i = 0; i < numImages; i++) {
   context.drawImage(
    image,
    0, 0, // source X, Y
    image.width, image.height, // source width and height
    offsetX + (i * scaledWidth), this.props.canvasHeight - layerHeight, // destination X, Y
    scaledWidth, layerHeight // destination width and height
   );
  }

  context.restore(); // Restore the context state
 }

Codeium at 8:05 am, Jun 6, 2024

To guard against an image with a width of 0 and prevent an infinite loop, you should verify that image.width is greater than 0 before proceeding with the drawing logic. If image.width is 0, it indicates that the image may not have loaded correctly. Here's how you can modify the drawParallaxLayer function:

drawParallaxLayer(context: CanvasRenderingContext2D, image: HTMLImageElement, scale: number, movementRate: number) {
  if (image.width === 0) {
    // Image is not loaded properly or has no width, so we shouldn't draw it
    console.error('Image has a width of 0, skipping drawing this layer');
    return;
  }

  const layerHeight = this.props.canvasHeight * scale;
  const scaledWidth = Math.max(1, image.width * scale); // Use Math.max to ensure non-zero width

  // Calculate how many times the image should be drawn to cover the canvas width
  const numImages = Math.ceil(this.props.canvasWidth / scaledWidth) + 1;

  // Calculate the offset for when the image scrolls
  const offsetX = -(this.state.backgroundOffsetX * movementRate) % scaledWidth;

  context.save(); // Save the current context state
  // context.globalAlpha = scale === 0.8 ? 0.5 : 0.6; // Adjust transparency for effect if desired

  // Draw the scaled image multiple times to cover the canvas width
  for (let i = 0; i < numImages; i++) {
    context.drawImage(
      image,
      0, 0, // source X, Y
      image.width, image.height, // source width and height
      offsetX + (i * scaledWidth), this.props.canvasHeight - layerHeight, // destination X, Y
      scaledWidth, layerHeight // destination width and height
    );
  }

  context.restore(); // Restore the context state
}

In this code:

  1. if (image.width === 0) checks if the image width is 0 and logs an error if true. The drawing operation is then skipped by returning early from the function.
  2. const scaledWidth = Math.max(1, image.width * scale); ensures that scaledWidth is at least 1, preventing division by zero when calculating numImages.
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