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Find Alpha value of specific pixel in image

usefroggyvoice

New member
Joined
Nov 9, 2017
Messages
4
I'm trying to check a specific x,y coordinate of a PNG image to determine if that pixel is transparent or not. From what I've been able to find it looks like I need to load the image into a DataBuffer then Peek the address of the coordinates I want to check. Is this anywhere near the right way to go? How would I translate an x and y coordinate to an address in a DataBuffer and check if it is transparent?
 
Ok, I would create an image as a render target, then you do a yourCanvas.ReadPixel to retrieve the values.
IF you want to read the image file into the databuffer, then you would need to make sure, it is and uncompressed file format so you can retrieve the values directly.
 
It is a compressed file format so reading it directly to a databuffer is out. The other method worked perfectly. Thank you Mike!

For reference:
Created an image as the render target for myCanvas
Draw the image to myCanvas
myCanvas.ReadPixels(x,y,1,1,DataBuffer)
Local rgba:Int = Buffer.PeekInt(0)
Local a:Int = (rgba Shr 24) & $ff 'Get The Alpha
If Int(a) = 0 Then pixel is transparent
if Int(a) = 1 then pixel is non-transparent
 
I didn't know you could read pixels like that in mojo2. My hack in original mojo was to clear the screen in white, set the colour to black, draw the image, read the pixel, shift the blue channel to alpha, and take its bitwise complement to get the original alpha component!
 
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