Re: DPU-414 terminal

[Thomas S. <t.s...@fz...>]

> That's a bit strange, because apparently it segfaulted in the 
> hidden-surface bookkeeping routines rather than anything having to do
> with bitmap management. I suppose one of those overflowed coordinates
> causes trouble in the depth-sort algorithm.

at least i have found what happens:
access to non-existing elements of 'quadtree' in procedure 'in_front' in
'hidden3d.c' resulting in useless values for 'listhead'

>    for (grid_x = grid_x_low; grid_x <= grid_x_high; grid_x ++)
>        for (grid_y = grid_y_low; grid_y <= grid_y_high; grid_y ++)
>            for (listhead = quadtree[grid_x][grid_y];    <<====THERE====

but why it happens - don't know.
the following patch prevents segfaults and gives warnings:

------------------------------------------------------------------------------

--- hidden3d.c.orig     2008-03-29 10:28:01.000000000 +0100
+++ hidden3d.c  2008-05-23 11:56:46.000000000 +0200
@@ -1801,5 +1801,21 @@
     grid_x_low = COORD_TO_TREECELL(xmin);
+    if (grid_x_low < 0) {
+        grid_x_low = 0;
+        fprintf(stderr,"in_front: grid_x_low set to 0\n");
+    }
     grid_x_high = COORD_TO_TREECELL(xmax);
+    if (grid_x_high >= QUADTREE_GRANULARITY) {
+        grid_x_high = QUADTREE_GRANULARITY-1;
+        fprintf(stderr,"in_front: grid_x_high set to
QUADTREE_GRANULARITY-1\n");
+    }
     grid_y_low = COORD_TO_TREECELL(ymin);
+    if (grid_y_low<0) {
+        grid_y_low = 0;
+        fprintf(stderr,"in_front: grid_y_low set to 0\n");
+    }
     grid_y_high = COORD_TO_TREECELL(ymax);
+    if (grid_y_high >= QUADTREE_GRANULARITY) {
+        grid_y_high = QUADTREE_GRANULARITY-1;
+        fprintf(stderr,"in_front: grid_y_high set to
QUADTREE_GRANULARITY-1\n");
+    }

------------------------------------------------------------------------------

gnuplot> set term pbm large size 100,100
gnuplot> set out 'test.pbm'
gnuplot> load 'singulr.dem'

in_front: grid_x_high set to QUADTREE_GRANULARITY-1
in_front: grid_y_high set to QUADTREE_GRANULARITY-1
in_front: grid_x_high set to QUADTREE_GRANULARITY-1
in_front: grid_y_high set to QUADTREE_GRANULARITY-1
...
Hit return to continue (1)
in_front: grid_x_high set to QUADTREE_GRANULARITY-1
in_front: grid_y_high set to QUADTREE_GRANULARITY-1
...

it seems that the 'xmax' and 'ymax' values, set in the macro 'setup_edge', 
are wrong sometimes.
-- 
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