To render a PNG image with transparent pixels using spine-webgl, you need to ensure that the transparent areas are handled correctly. Here is a step-by-step guide to achieve this:

1. Load the PNG Image:

      assetManager.loadTexture("mybackground.png");
      let texture = assetManager.require("mybackground.png");

2. Render the Image:
   In your render() function, you need to ensure that the WebGL context is set up to handle transparency correctly. This involves enabling blending and setting the appropriate blend function.

      function render() {
          // Begin rendering
          canvas.renderer.begin();
   
          // Enable blending
          let gl = canvas.renderer.context;
          gl.enable(gl.BLEND);
          gl.blendFunc(gl.SRC_ALPHA, gl.ONE_MINUS_SRC_ALPHA);
   
          // Draw the texture
          canvas.renderer.drawTexture(texture, x, y, width, height);
   
          // End rendering
          canvas.renderer.end();
      }

3. Ensure Correct Color Handling:
   If you are using drawTextureRotated and facing issues with transparency, make sure that the color parameter is set correctly. You can use new spine.Color(1, 1, 1, 1) to ensure the image is rendered with its original colors and transparency.

      canvas.renderer.drawTextureRotated(texture, x, y, width, height, rotation, new spine.Color(1, 1, 1, 1));

By following these steps, you should be able to render a PNG image with transparent pixels correctly using spine-webgl.