source: thomson/code/C/F14/waves.c@ 1180ce9

// Here's the trick:
//  - unpack the logo to screen memory
//  - The color RAM doesn't move. Part with the logo is shown as expected,
//  below it is an area of single color (we can use the forme part without
//  visible artifacts)
//  - The pixel RAM has the visible copy of the logo, and an hidden copy of the
//  waving part below it
//  - We run over the logo lines, pick from the invisible part and copy to the 
//  visible one
//  - Easy way: only vertical ondulations are done.
//  - To do horizontal ondulations, we'd need 8 versions of the logo, each
//  shifted one byte from the previous. This would fill a lot of RAM !

#include <effect.h>

extern unsigned char SIN[256];

asm("\n"
"       .area .text \n"
"       INCLUDEBIN ../LOGO01.CRU \n"
"forme_logo             \n"
);

void init_L()
{
        // TODO clear screen to white
        couleur();
        for(unsigned int* i = (unsigned int*)(0); i < (unsigned int*)8000; i++)
        {
                *i = 0x7777;
        }
        
        forme();

        asm("\n"
"               LDY             #5000                   \n"
"               LDU             #forme_logo-1   \n"
"               LBSR    exo2                    \n"
        :::"x", "y");

        // Copy the bottom part of the logo to the top of the screen (pixels only)
        // We will use this as a source for distorting the actual logo below.
        unsigned int* src;
        unsigned int* dest;
        dest = (unsigned int*)1280;
        for(src = (unsigned int*)5000; src >= (unsigned int*)3720;)
                *dest-- = *src--;

        couleur();

        for(int y = 2280; y < 3560; y+=40)
        {
                for(int x = 0; x < 40; x+=2)
                        *(unsigned int*)(x+y) = 0x0707;
                for(int x = 20; x < 28; x+=2)
                        *(unsigned int*)(x+y) = 0x1717;
        }

        for(int y = 3560; y < 5000; y+=40)
        {
                for(int x = 0; x < 40; x+=2)
                        *(unsigned int*)(x+y) = 0x8787;
                for(int x = 20; x < 28; x+=2)
                        *(unsigned int*)(x+y) = 0x9797;
        }

        forme();

        return;
}


void draw_L(int frame)
{
        for(int y = 0; y < 32; y++)
        {
                int offset = (y + (SIN[((y+frame)*4) & 0xFF] >> 6)) * 40;
                for(int x = 0; x < 40; x++) {
                        *(unsigned int*)(x + y * 40 + 3720) =
                        *(unsigned int*)(x + offset);
                }
        }

        asm("\n"
"z      TST     0xA7E7  \n"
"       BMI z           \n"
"bb     TST     0xA7E7  \n"
"       BPL bb          \n"
        );
}