crsn/examples/bmp-parser.csn

(
    ; This program parses and shows bmp. 
    ; Only 32-bit RGB format is supported at the moment.
    ;
    ; To run it: 
    ;    cat pika-rgb32.bmp | crsn bmp-parser.csn
    
    (def HUGEPIXELS 1)

    (ld r0 @cin_r)(cmp r0 'B' (ne? (fault "Bad magic")))
    (ld r1 @cin_r)(cmp r1 'M' (ne? (fault "Bad magic")))
    (ldn _ @cin_r 8)
    
    (sym datastart r6)
    (call rd4) (ld datastart res0)
    
    (sym hlen r7)
    (call rd4) (ld hlen res0)
    
    (sym w r8) (sym h r9)
    (call rd4) (ld w res0)
    (call rd4) (ld h res0)
    
    (ldn _ @cin_r 2) ; planes
    
    (sym bits r10)
    (call rd2) (ld bits res0)
    
    (call rd4) (tst res0 (nz? (fault "Compression not implemented")))
    (ldn _ @cin_r 12) ; image size + resolutions
    
    (sym usedcolors r11)
    (call rd4) (ld usedcolors res0)
    (ldn _ @cin_r 4) ; read to the end of the 40-byte header
    
    (cmp bits 32 (ne? (fault "Only 32-bit supported now")))
    
    ; Skip the palette if any
    (ld r0 datastart)
    (sub r0 54)
    
    ; Discard bytes until the start of image data. This contains the palette!
    ; TODO load to a buffer when indexed BMP support is added
    (ldn _ @cin_r r0)
    
    (sym x r4)
    (sym y r5)
    (sym dy r12)
    (ld x 0)(ld y h)(ld dy -1)(dec y)
    
    ; test if height is negative
    (and r0 h 0x8000_0000
        (nz? 
            (se32 h) ; sign extend to u64
            (mul h -1)
            (ld dy 1) ; going downward
            (ld y 0)
            (dec y)
        ))
    
    (ld r0 w)(ld r1 h)
    (tst HUGEPIXELS (z? (j :nohuge1)))
    (mul r0 8)(mul r1 8)(sub r1 8)
    (:nohuge1)
    (sc-init r0 r1)
    
    ; Here comes the parsing
    
    (:nx)
        (call rd4)  
        (tst HUGEPIXELS 
            (z? (sc-px x y res0))
            (nz? (call bigpixel x y res0)))
        (add x 1)
        (cmp x w (ne? (j :nx)))
        (ld x 0)
        (add y dy (z? (j :end)))
        (cmp y h (eq? (j :end)))
        (j :nx)
    
    (:end)
        (sc-blit)
    (:endl)
        (sc-poll)
        (mslp 10)
        (j :endl)
        
    (proc bigpixel x y rgb
        (ld r4 x)(ld r1 y)(sub r1 1)
        (mul r4 8)(mul r1 8)
        (ld r2 r4)(add r2 8)
        (ld r3 r1)(add r3 8)
        (ld r0 r4)
        (:nx)        
            (sc-px r0 r1 rgb)
            (add r0 1)
            (cmp r0 r2 (ne? (j :nx)))
            (ld r0 r4)
            (add r1 1)
            (cmp r1 r3 (eq? (ret)))
        (j :nx)    
    )
    
    (proc rd4
        ; Read 4 bytes as little endian
        (ld8 r0 @cin_r)
        (ld8/8 r0 @cin_r)
        (ld8/16 r0 @cin_r)
        (ld8/24 r0 @cin_r)
        (ret r0)
    )
    
    (proc rd2
        ; Read 2 bytes as little endian
        (ld8 r0 @cin_r)
        (ld8/8 r0 @cin_r)
        (ret r0)
    )
)