- moved to seldes.pp

docs/go32ex/seldes.pp

@@ -0,0 +1,101 @@
+Program sel_des;
+
+uses crt,
+     go32;
+
+const maxx = 80;
+      maxy = 25;
+      bytespercell = 2;
+      screensize = maxx * maxy * bytespercell;
+
+      linB8000 = $B800 * 16;
+
+type string80 = string[80];
+
+var
+    text_save : array[0..screensize-1] of byte;
+    text_oldx, text_oldy : Word;
+
+    text_sel : Word;
+
+procedure status(s : string80);
+begin
+  gotoxy(1, 1); 
+  clreol; 
+  write(s); 
+  readkey;
+end;
+
+procedure selinfo(sel : Word);
+begin
+gotoxy(1, 24);
+clreol; 
+writeln('Descriptor base address : $', 
+        hexstr(get_segment_base_address(sel), 8));
+clreol; 
+write('Descriptor limit : ', 
+       get_segment_limit(sel));
+end;
+
+function makechar(ch : char; color : byte) : Word;
+begin
+     result := byte(ch) or (color shl 8);
+end;
+
+begin
+seg_move(dosmemselector, linB8000, 
+         get_ds, longint(@text_save), screensize);
+text_oldx := wherex; text_oldy := wherey;
+seg_fillword(dosmemselector, linB8000, 
+             screensize div 2, 
+             makechar(' ', Black or (Black shl 4)));
+status('Creating selector ' + 
+        '''text_sel'' to a part of text screen memory');
+text_sel := allocate_ldt_descriptors(1);
+set_segment_base_address(text_sel, linB8000 
+                          + bytespercell * maxx * 1);
+set_segment_limit(text_sel, 
+                  screensize-1-bytespercell*maxx*3);
+selinfo(text_sel);
+
+status('and clearing entire memory ' + 
+       'selected by ''text_sel'' descriptor');
+seg_fillword(text_sel, 0, 
+             (get_segment_limit(text_sel)+1) div 2, 
+             makechar(' ', LightBlue shl 4));
+
+status('Notice that only the memory described'+
+       ' by the descriptor changed, nothing else');
+
+status('Now reducing it''s limit and base and '+
+       'setting it''s described memory');
+set_segment_base_address(text_sel, 
+     get_segment_base_address(text_sel) 
+     + bytespercell * maxx);
+set_segment_limit(text_sel, 
+     get_segment_limit(text_sel) 
+     - bytespercell * maxx * 2);
+selinfo(text_sel);
+status('Notice that the base addr increased by '+
+       'one line but the limit decreased by 2 lines');
+status('This should give you the hint that the '+
+       'limit is relative to the base');
+seg_fillword(text_sel, 0, 
+             (get_segment_limit(text_sel)+1) div 2, 
+             makechar(#176, LightMagenta or Brown shl 4));
+
+status('Now let''s get crazy and copy 10 lines'+
+       ' of data from the previously saved screen');
+seg_move(get_ds, longint(@text_save), 
+         text_sel, maxx * bytespercell * 2, 
+         maxx * bytespercell * 10);
+
+status('At last freeing the descriptor and '+
+       'restoring the old screen contents..');
+status('I hope this little program may give '+
+       'you some hints on working with descriptors');
+free_ldt_descriptor(text_sel);
+seg_move(get_ds, longint(@text_save), 
+         dosmemselector, linB8000, screensize);
+gotoxy(text_oldx, text_oldy);
+end.