click all texture except alpha

When you recive the mouse down event figure out what button is getting clicked, then adjust the position based on the button, example, if the button is located at (150, 200) and the click is at (163, 220) then subtract the button position from the X and Y positions to get the spot on the button that got clicked (13, 20). Then you need to check if that pixel is transparent. You can either lock the texture and then check the alpha value of that pixel to see if it is zero, or generate an alpha map, just an array of boolean values the size of the number of pixels of that texture that is either 1 for a solid pixel, and 0 for a transparent pixel. The alpha map would be generated when the texture was loaded. The first option would be best for button clicks, but the locking and unlocking texture memory is slow, so if you wanted to do this for a mouse over you would probably want to go with the second option.

OK, Thanks. But do you know how I generate a boolean-style mask for all transparent pixels.

My little game ala Monkey Island needs to have lots of this stuff, both for collision detection, and selection (mouse over and mouse click), so I dont want to hand code the masks for all pixels in every D3DXSprite. The 'lock texture and check if the a visible or transparent pixel is clicked'-method sounds nice but may be alitle hevey if I got 10 sprites with different (non boxy) shapes.

Is there not a way to just load the textue and say that the transparent pixels could not be clicked, just like they could not be seen.

Please give me any hints on how to do this, tho is a keypart of my game. and again, I'm useing vb/dx8/d3dxsprites to draw all textures.

Thanks

[edited by - lexor on May 22, 2002 7:00:46 PM]

No, you can''t specify an unclickable area. Solid pixel maps work fast though, I use this for my collision detection in the game I''m working on now. It''s written in C++, but I''ll give you the basic idea. Every texture I have has a structure associated with it. That structure stores information about the texture pointer, the source rect, the rotation, etc. It also contains a pointer to an solid pixel mask. I don''t know if you are forcing one texture format to be used, I''m not, but it is a lot easier if you don''t have to code for every possible texture format. For this example I''ll use 32 bit textures in the A8R8G8B8 format. First you load the texture, then you lock the whole texture to get access to the bits. As long as all you are trying to find is the alpha value being zero you can just grab four bytes at a time from the locked bits, then use something like this to see if the pixel is transparent.

''Lock the texture, ReDim boolean array to lHeight by lWidth
''Copy one pixel at a time to a long variable
''Check the alpha value of the pixel
If (lPixel And &HFF000000) = 0 Then
   ''...The pixel is tranparent
   Surface.pSolidPixelMap(lCountHeight, lCountWidth) = false
Else
   ''Solid pixel
   Surface.pSolidPixelMap(lCountHeight, lCountWidth) = true
End If
''Unlock the texture
 

When mouse click over button

If Button.Surface.pSolidPixelMap(X, Y) = true Then
    ''Click the button.
    ...
End If
 

Hope this helps.