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     BITBLT(9.3)                                           BITBLT(9.3)

          Code, addr, bitblt, point, rectf, screenswap, segment,
          texture - basic jerq graphics functions

          #include <jerq.h>

          typedef int Code;
          Code F_STORE, F_XOR, F_OR, F_CLR;

          Word *addr(b, p) Bitmap *b; Point p;

          void bitblt(sb, r, db, p, f) Bitmap *sb, *db; Rectangle r;
          Point p; Code f;

          void point(b, p, f) Bitmap *b; Point p; Code f;

          void rectf(b, r, f) Bitmap *b; Rectangle r; Code f;

          void screenswap(b, r, s) Bitmap *b; Rectangle r, s;

          void segment(b, p, q, f) Bitmap *b; Point p, q; Code f;

          void texture(b, r, t, f) Bitmap *b; Rectangle r; Texture *t;
          Code f;

          The type Code defines the constants passed to the graphics
          primitives to indicate the Boolean operation to be performed
          on the source and destination.  The meanings of a Code are:

               F_STORE        target =  source
               F_OR           target |= source
               F_XOR               target ^= source
               F_CLR               target &= ~source

          In other words, if a Rectangle is copied to another place
          with Code F_OR, the result will be the bitwise OR of the
          contents of the source Rectangle and the target area.  For
          operations with no explicit source, such as line drawing,
          the source is taken to be an infinite bitmap with zeroes
          everywhere except on the object (e.g. line) generated by the
          operator, with coordinates aligned with the destination bit-
          map.  F_STORE is the same as F_OR for non-rectangular opera-

          Addr returns the address of the Word containing the bit at
          Point p in the Bitmap b.

          Bitblt (bit-block transfer) copies the data in Rectangle r

     BITBLT(9.3)                                           BITBLT(9.3)

          in Bitmap sb to the congruent Rectangle with origin p in
          Bitmap db. The nature of the copy is specified by the Code

          Point draws the pixel at location p in the Bitmap b accord-
          ing to Code f.

          Screenswap does an in-place exchange of the on-screen Rect-
          angle s and the Rectangle r within the Bitmap b. Its action
          is undefined if r and s are not congruent.  The Rectangle s
          is not clipped to the Bitmap b, only to the screen.

          Segment draws a line segment in Bitmap b from Point p to q,
          with Code f. The segment is half-open: p is the first point
          of the segment and q is the first point beyond the segment,
          so adjacent segments sharing endpoints abut.  Like all the
          other graphics operations, segment clips the line so that
          only the portion of the line intersecting the bitmap is dis-

          Texture draws with function specified by f in the Rectangle
          r, in the Bitmap b, the Texture specified by t. The texture
          is replicated to cover r. Rectf is equivalent to texture
          with *t set to all one's.

          In the above definitions, the type Bitmap may be replaced
          with Layer anywhere; see newlayer(9.2).