[pygame] Mode 7 Demo

[Kris Schnee <kschnee@xxxxxxxxxx>]

I put together a quick-and-dirty demo of a "Mode 7" pseudo-3D effect. I 
have no specific plans for it, but it looks neat. The framerate is bad. 
Thoughts?

Screenshot at <http://kschnee.xepher.net/pics/080126_mode7.jpg>.
Example of the effect in "Secret of Mana": 
<http://mmxz.zophar.net/rpg/mana2/images/flammie.gif>

Kris

"""
Quick demo of a "Mode 7" pseudo-3D effect,
as seen in some 16-bit-era video games.
"""

import pygame
screen = pygame.display.set_mode((800,600))

ground = pygame.image.load("landscape.bmp") ## 1000x1000 works
sky = pygame.image.load("sky.png") ## At least 800x300

## Fog @ horizon.
fog = pygame.surface.Surface((800,20)).convert_alpha()
for y in range(20):
    a = 200 - (10*y)
    pygame.draw.rect(fog,(255,255,255,a),(0,y,800,5))

class Mode7:
    def __init__(self,**options):
        self.sky = options.get("sky")
        self.ground = options.get("ground")
        self.fog = options.get("fog")
        ## "Location" of the top-left part we'll draw.
        self.ground_x, self.ground_y = options.get("coords",(0,0))
        self.movement = options.get("movement",(3,3))

    def Draw(self):
        stretch_factor = 200.0 ## Try eg. 75.0 also
        for y in range(300,600):
            ## Take a line from the original & stretch it.
            img_y = (y+self.ground_y-300) * 2
            line = pygame.surface.Surface((800,1))
            line.blit(self.ground,(0,0),(self.ground_x,img_y,800,1))
            w = 800 * (1.0 + ((y-300)/stretch_factor) )
            x = -(w-800)/2 ## Draw wide line left of screen's edge
            line = pygame.transform.scale(line,(w,1))
            screen.blit(line,(x,y))
        screen.blit(self.sky,(0,0),(200,0,800,300))
        screen.blit(self.fog,(0,300))

    def Go(self):
        for n in range(40):
##            screen.fill((0,0,0)) ## Not needed; screen is filled
            self.Draw()
            pygame.display.update()
            self.ground_x += self.movement[0]
            self.ground_y += self.movement[1]


m7 = Mode7(sky=sky,ground=ground,fog=fog)
m7.Go()