At level 13, casting Zo Kath Ra<\/em> spell to open the wall should free the power gem \u2014 but the wall stayed completely unresponsive.<\/p>\n Cause:<\/strong><\/p>\n The Fix:\u00a0 <\/strong>updating Next I implemented Before:<\/strong><\/p>\n After: Before: After: Before:<\/strong> After:<\/strong> Enabled palette translation in A spell stone kept on ground:<\/p>\n When viewed from a distance of 2 tiles, it looks: After<\/strong> (with Palette translation):<\/strong><\/p>\n Restarting after your party is dead would result in a crash with buffer overflow.<\/p>\n Cause:<\/strong>\u00a0 On restart, Fix:\u00a0 <\/strong>Track each thing type’s allocated capacity in Some places in the code used Fix:<\/strong> Replaced those with Another instance,<\/p>\n On the 16th iteration the value overflowed the int type, causing signed integer overflow.<\/p>\n Fix:<\/strong> changed Cause:<\/strong>\u00a0 Doing a bitwise-AND directly on ScummVM’s 1 byte per pixel format corrupts the resulting color palette index. The combined indexes produced garbage color index numbers, leading to severely corrupted\/incorrect pixel colors on the screen<\/p>\n Fix:<\/strong>\u00a0 Rewrote the logic to pick the mask color directly if it isn’t white, or fall back to the source pixel if it isn’t transparent.<\/p>\n Cause:<\/strong> The highlight screen box was using an XOR mask of Fix:<\/strong>\u00a0 Changed the mask to Before:<\/strong><\/p>\n After: Issue:<\/strong> \u00a0 Proper Fix:<\/strong>\u00a0 As Sev suggested, I would parse the file data on load directly into arrays of structs, so the engine can just address those structs directly instead of re-parsing every time. This time it won’t take much time as I’m already familiar with the places these macros are used.<\/p>\n That was it for this week. The DM engine work will be finished in a day or two \u2014 till then, goodbye \ud83d\ude42<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":" Hi everyone, this is week 5 of my GSoC project. Work on the Dungeon Master engine is almost at an end \u2014 except for one last hurdle, which I’ll discuss later. The Unresponsive Wall At level 13, casting Zo Kath Ra spell to open the wall should free the power gem \u2014 but the wall […]<\/p>\n","protected":false},"author":30,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[9],"tags":[],"class_list":["post-230","post","type-post","status-publish","format-standard","hentry","category-week-5"],"_links":{"self":[{"href":"https:\/\/blogs.scummvm.org\/mohit\/wp-json\/wp\/v2\/posts\/230","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blogs.scummvm.org\/mohit\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blogs.scummvm.org\/mohit\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blogs.scummvm.org\/mohit\/wp-json\/wp\/v2\/users\/30"}],"replies":[{"embeddable":true,"href":"https:\/\/blogs.scummvm.org\/mohit\/wp-json\/wp\/v2\/comments?post=230"}],"version-history":[{"count":55,"href":"https:\/\/blogs.scummvm.org\/mohit\/wp-json\/wp\/v2\/posts\/230\/revisions"}],"predecessor-version":[{"id":299,"href":"https:\/\/blogs.scummvm.org\/mohit\/wp-json\/wp\/v2\/posts\/230\/revisions\/299"}],"wp:attachment":[{"href":"https:\/\/blogs.scummvm.org\/mohit\/wp-json\/wp\/v2\/media?parent=230"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blogs.scummvm.org\/mohit\/wp-json\/wp\/v2\/categories?post=230"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blogs.scummvm.org\/mohit\/wp-json\/wp\/v2\/tags?post=230"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}![\"\"](\"https:\/\/blogs.scummvm.org\/mohit\/wp-content\/uploads\/sites\/82\/2026\/06\/Level-13-zo-kath-ra.png\")
<\/p>\nfor (thingBeingProcessed = squareFirstThing; thingBeingProcessed != _vm->_thingEndOfList; thingBeingProcessed = dungeon.getNextThing(thingBeingProcessed)) {\r\n\t\tThing lastProcessedThing = thingBeingProcessed;\r\n<\/pre>\nlastProcessedThing<\/code> pointer was being updated to thingBeingProcessed<\/code> at the start of each iteration. Before unlinking this particular sensor, the code checks if (lastProcessedThing == thingBeingProcessed)<\/code>. Since both pointed to the same thing, this check always failed and the sensor was never unlinked, failing to trigger the next sensor.<\/p>\nlastProcessedThing<\/code> to thingBeingProcessed<\/code> before updating thingBeingProcessed<\/code> resolved the issue.<\/p>\n![\"\"](\"https:\/\/blogs.scummvm.org\/mohit\/wp-content\/uploads\/sites\/82\/2026\/06\/Level-13-zo-kath-ra-done.png\")
<\/p>\nShade Screen Box<\/span><\/h4>\n
DisplayMan::shadeScreenBox<\/code>. It draws a checkerboard pattern over a given box by coloring every other pixel based on alternating coordinates, creating a semi-transparent shading overlay on top of whatever was already drawn there, graying out menus or buttons.<\/p>\n![\"\"](\"https:\/\/blogs.scummvm.org\/mohit\/wp-content\/uploads\/sites\/82\/2026\/06\/Shadescreen-before-1024x654.png\")
<\/p>\n![\"\"](\"https:\/\/blogs.scummvm.org\/mohit\/wp-content\/uploads\/sites\/82\/2026\/06\/Shadrescreen-after-1024x658.png\")
<\/strong><\/p>\n![\"\"](\"https:\/\/blogs.scummvm.org\/mohit\/wp-content\/uploads\/sites\/82\/2026\/06\/shadescreen-1.png\")
<\/strong><\/p>\n![\"\"](\"https:\/\/blogs.scummvm.org\/mohit\/wp-content\/uploads\/sites\/82\/2026\/06\/shadescreen-3.png\")
<\/strong><\/p>\n![\"\"](\"https:\/\/blogs.scummvm.org\/mohit\/wp-content\/uploads\/sites\/82\/2026\/06\/shadescreen-2.png\")
<\/p>\n![\"\"](\"https:\/\/blogs.scummvm.org\/mohit\/wp-content\/uploads\/sites\/82\/2026\/06\/shade-screen-4.png\")
<\/p>\nFix blitToBitmapShrinkWithPalChange()<\/span><\/h4>\n
blitToBitmapShrinkWithPalChange<\/code> by mapping each source pixel through the translation table and dividing by 10 to account for the original game’s 10-multiplier scale.<\/p>\n![\"\"](\"https:\/\/blogs.scummvm.org\/mohit\/wp-content\/uploads\/sites\/82\/2026\/06\/zokathra.png\")
<\/p>\n
\nBefore (without Palette translation):<\/strong><\/p>\n![\"\"](\"https:\/\/blogs.scummvm.org\/mohit\/wp-content\/uploads\/sites\/82\/2026\/06\/zokathra-before.png\")
<\/p>\n![\"\"](\"https:\/\/blogs.scummvm.org\/mohit\/wp-content\/uploads\/sites\/82\/2026\/06\/zo-kath-ra-after.png\")
<\/h4>\nSegfault on restart<\/span> <\/span><\/h4>\n
loadDungeonFile()<\/code> was skipping reallocation to reuse existing buffers \u2014 but if the new dungeon needed more space than what was previously allocated, writes would go out of bounds.<\/p>\n_allocatedThingCounts<\/code>. On restart, if the new dungeon’s count exceeds what was previously allocated, reallocate and update the tracked limit<\/p>\nRuntime errors<\/span><\/h4>\n
<<<\/code> on signed integers, which is undefined behavior in C++ when the value is negative.<\/p>\n*<\/code> to get the same result safely.<\/p>\nint16 attribMask = 1;\r\nfor (uint16 stringIndex = 0; stringIndex < 16; stringIndex++, attribMask <<= 1) {\r\n<\/pre>\nattribMask<\/code> to uint16<\/code><\/p>\nFixing blitBoxFilledWithMaskedBitmap()<\/span><\/h4>\n
*nextDestPixel = *mask & nextSrcPixel;<\/pre>\n
Spellcasting Tabs Display<\/span><\/h4>\n
0x0F<\/code>, but only the 3rd bit needed to be flipped, producing the wrong highlight color on the spellcasting tabs.<\/p>\n0x04<\/code>.<\/p>\n![\"\"](\"https:\/\/blogs.scummvm.org\/mohit\/wp-content\/uploads\/sites\/82\/2026\/06\/Spellcasting-tab-before.png\")
<\/p>\n![\"\"](\"https:\/\/blogs.scummvm.org\/mohit\/wp-content\/uploads\/sites\/82\/2026\/06\/Spellcasting-tab-after.png\")
<\/strong><\/p>\nThe <\/span>one last hurdle<\/span><\/h4>\n
loadDungeonFile()<\/code> reads Big-Endian file data and stores it into _thingData<\/code> as native-endian uint16s<\/code>. But the gameplay macros like DOOR_nextThing<\/code> access this memory using READ_LE_UINT16<\/code> and WRITE_LE_UINT16<\/code>, which always expect Little-Endian memory layout. On Big-Endian machines this setup won’t work.<\/p>\n