add bmp parser example

examples/bmp-parser.csn

@@ -0,0 +1,125 @@
+(
+    ; This program parses and shows bmp. 
+    ; Only 32-bit RGB format is supported at the moment.
+    
+    (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 0x80000000 
+        (nz? 
+            (or h 0xFFFFFFFF_00000000) ; sign extend
+            (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)(lsl r0 8)
+        (ld8 r0 @cin_r)(lsl r0 8)
+        (ld8 r0 @cin_r)(lsl r0 8)
+        (ld8 r0 @cin_r)
+        (sw32 r0)
+        (rev r0)
+        (ret r0)
+    )
+    
+    (proc rd2
+        ; Read 2 bytes as little endian
+        (ld8 r0 @cin_r)(sw8 r0)
+        (ld8 r0 @cin_r)(sw8 r0)
+        (ret r0)
+    )
+)
+
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