Re: [SPAM: 8.000] [pygame] Pygame 2.0 software blits

[Lenard Lindstrom <len-l@xxxxxxxxx>]

On 14-03-04 01:29 AM, Greg Ewing wrote:
> Lenard Lindstrom wrote:
> > If the bytecode is exposed at the Python end then any expression can 
> > be encoded, a different one for each channel if desired. Conceivably, 
> > a Python expression, or function, could be compiled into a blit 
> > operation.
>
> That would be even more awesome!
How does this look as an example:

def alpha_blend(source, target):
    """pygame.Surface.blit alpha blit blend

        blit_blend(Color, Color) => Color

        return a new target pixel value

    """
    source_alpha = source.a
    target.r = element_blend(source.r, target.r, source_alpha)
    target.g = element_blend(source.g, target.g, source_alpha)
    target.b = element_blend(source.b, target.b, source_alpha)
    target.a = alpha_element_blend(source_alpha, target.a)
    return target

def element_blend(source, target, alpha):
    return (((source - target) * alpha + source) >> 8) + target

def alpha_element_blend(source, target):
    return source + target - ((source * target) // 255)

"""
>>> from pygame import Color
>>> print alpha_blend(Color('red'), Color('green'))
(255, 0, 0, 255)
>>> print alpha_blend(Color(255, 0, 0, 128), Color('green'))
(128, 127, 0, 255)
>>> print alpha_blend(Color('red'), Color(0, 255, 0, 128))
(255, 0, 0, 255)
>>> print alpha_blend(Color(255, 0, 0, 128), Color(0, 255, 0, 128))
(128, 127, 0, 192)
>>>
"""

This shows how the blend function can be tested in Python. For the JIT, 
arguments are treated as pass-by-value, so changes to 'target' will not 
affect the target surface. Instead, the target pixel is set to the 
function's return value.

The Python function is traced to generate JIT code. For now, branching 
and recursion are unsupported. The JIT takes care of adding the row and 
column loops.

Inspired by PyPy RPython.

Lenard Lindstrom