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Translucent Textures with Darkness Weather

Author(s): MrHam88.
Implementation: Trifindo.

This is a guide on resolving rendering issues for 'intermediate alpha' (translucent) textures that are used in HeartGold Version or SoulSilver Version games where the header's weather is "Darkness" (i.e. limited visibility until the move Flash is used).

Symptoms​

Translucent textures render inconsistently, some polygons render completely opaque and black, others invisible. The below screenshot shows the correctly rendered effect on the left, and the symptom of the issue on the right from the entrance to Dark Cave in HeartGold Version.

Conditions of Issue Occurring​

Occurs when the following conditions are met:

  1. The header's default weather is set to 11 (Darkness) or 12 (Darkness after flash), or the header's weather can be changed to one of these values through scripting or events.
  2. The vanilla or modified Areadata (maps .nsbtx) contains one or more materials that use either of the A3I5 or A5I3 colour format values.
  3. A custom map (converted from .imd to .nsbmd file either directly, or via map creation in PDSMS) is being loaded that contains one or more faces/polygons using one of these materials.

An example would be a custom map of Cerulean Cave, which has two materials light and f_kage that use A3I5/A5I3 colour format, in the light above the cave entrance, and the shadow underneath a bridge.

Root Cause​

The material_array section of the .imd file requires translucent materials of this kind of have a specific polygon_id value, in order for the correct transluency attributes to be set in the .nsbmd file. When building maps in PDSMS, it appears that the polygon_id value is always set to 0 by the tool.
A polygon_id value of 8 is required to correctly convert the translucency behaviour for these materials.
This is likely something that is set correctly for all translucent materials wherever they are used in the vanilla games, but there is no visible impact of PDSMS not setting it in most cases.

Understanding the Root Cause​

  • The g3dcvtr.exe converter that PDSMS uses to produce Nitro System Binary output files (such as .nsbmd map files) can also be used to return some information on these files.
  • By placing an .nsbmd file in the same directory as the converter, and then running the converter using a command line utility (e.g. Windows PowerShell), an output file can be returned.
  • Comparing the outputs of these two files (for example between a vanilla map file and a custom recreation) provides context on specific differences.
  • The PolygonAttr hex value returned provides details on the various parameters within the file for a given material definition.
    • An outline of these attributes can be found here.
    • As can be seen from the above resource, the 24-29th bits of the 32-bit value include information for translucent materials (it is specifically bit 27).
    • An easy visualisation of how the hex value relates to specific bits can be obtained by pasting the hex into a tool such as the tomeko binary/hex converter.
  • To inform the converter to set this bit correctly during .nsbmd creation, a polygon_id of 8 is required in the .imd file.

Steps to Resolve​

  1. Export the map to OBJ in PDSMS.
  2. Convert the map from OBJ to IMD in PDSMS.
  3. Open the .imd file in a text editor (Notepad++ or VScode for example).
  4. Find the translucent material by name in the material_array.
  5. Replace the associated polygon_id of 0 with a value of 8.
  6. Save the .imd file.
  7. Convert the map from IMD to NSBMD in PDSMS (or by directly dragging the .imd onto the g3dcvtr.exe converter)

A precise and quick method of completing steps 4 and 5 is to use a find and replace function to find a string of text long enough to be unique to only the materials in question. For example for a material called "light", this string could be searched for: name="light" polygon_id="0" and replaced with this string: name="light" polygon_id="8".