shithub: jbig2

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jbig2dec: Fix composing subset of image onto destination.

--- a/jbig2_image.c

+++ b/jbig2_image.c

@@ -259,10 +259,29 @@

     if (src == NULL)

         return 0;

-    if (op != JBIG2_COMPOSE_OR) {

+    /* The optimized code for the OR operator below doesn't

+       handle the source image partially placed outside the

+       destination (above and/or to the left). The affected

+       intersection of the destination is computed correctly,

+       however the correct subset of the source image is not

+       chosen. Instead the upper left corner of the source image

+       is always used.

+

+       In the unoptimized version that handles all operators

+       (including OR) the correct subset of the source image is

+       chosen.

+

+       The workaround is to check whether the x/y coordinates to

+       the composition operator are negative and in this case use

+       the unoptimized implementation.

+

+       TODO: Fix the optimized OR implementation if possible. */

+    if (op != JBIG2_COMPOSE_OR || x < 0 || y < 0) {

         /* hand off the the general routine */

         return jbig2_image_compose_unopt(ctx, dst, src, x, y, op);

     }

+

+    /* optimized code for the prevalent OR operator */

     /* clip */

     w = src->width;