How to get pixel transparency of scaled up image?

pcastro128

I’m using Processing.py 3, and I want to be able to detect when the mouse is over a specific image, but also on a pixel that isn’t transparent. I think doing img.get() would give me the info I need, but I’ve also scaled up the image. How would I go about doing this?

For example: I have an image, whose original size is 10x10 pixels, scaled up by 10 so on the screen it’s 100x100. It’s placed at x=100, y=100. The mouse is located at x=150, y=150. What code would I need to get a true/false on the transparency of the image at the mouse position?

I looked at the documentation but it’s a little unclear. I also don’t know how to access alpha data.

Here’s my guess(in python mode):

test_img = loadImage(“image.png”)
image(img, 100, 100, 100, 100)

def if_mouse_on_image(img, xpos, ypos):
    mouse_on_image_x = mouseX - xpos
    mouse_on_image_y = mouseY - ypos

    pixel_data = img.get(mouse_on_image_x, mouse_on_image_y, 10, 10) #here is where I’m confused the most. 
    return not pixel_data[3] #is this correct? I’m not familiar with alpha values

print(if_mouse_on_image(test_img))

Would this code achieve my goals? The reason I haven’t tried this myself is because I’m not at my computer. I’m writing this from my phone.

pcastro128

I don’t know why the code section freaked out.

Chrisir

You can go back

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koogs

(done)

pcastro128

Thank you koogs. Any comment on the question?

koogs

Python mode? No

Try drawing a rectangle of known colour / alpha and the getting the pixels from that to see how they are stored. In Java the pixels are ARGB, one byte per channel = one int per pixel.

pcastro128

Thank you again! I worked out the problem from your comment.

jeremydouglass

Python mode is ARGB bytes as well -- I believe the underlying pixels[] implementation is the Java API running on Jython.

See also alpha and tint:

• http://py.processing.org/reference/alpha.html
• http://py.processing.org/reference/tint.html

pcastro128

Yep. Python mode has almost the exact same features as java mode.