Entry 54

Stream 2's ribbons morph: ccMorpher::Modify ported, the tendrils around the figure

2026-09-23rendertest

Filescrates/piney-data/src/model.rscrates/piney-draw/src/lib.rscrates/piney-gs/src/convert.rscrates/piney-desktop/src/soft.rscrates/piney-stream/src/draw.rsdocs/engine/stream.md

The user remembered animated lines in event 1's first cutscene (stream 2), where the port drew four straight brown bands that only moved with the figure. 52 had left F_Morpher decoded but not drawn.

Finding it

• Where the ribbons come from. OBJ_ribbon_a00-d00 draw models from the preload file str0001e. That file has one frame, so nothing in their own records changes their shape.
• The morphers. Stream 2 holds four morphers, MPH_ribbon_a00-d00. Each blends two targets, MDL_ribbon_*39 and *40, with weights such as 0.4 and 0.6 that the F_Morpher records change frame by frame. Each ribbon's Obj2 names its morpher as its modifier.
• The rest of the stream's effects. Func_str0001 (3,400 bytes) directs them: ccRasterNoize, ccBufferSampling feedback, ccBufferReverce, fades and fog, cued by the stream's notes. It does not touch the ribbons, and it is still not ported.

ccMorpher::Modify (0x0013af10)

ccModel::Draw calls its modifier for each rigid mmat before the packets. Modify writes the blended positions to a work buffer that stands in for the mmat's own:

1. Rescale. A target whose vertex scale differs is brought to the base model's, once and in place: trunc(v * target / base).
2. Weights. Each weight becomes 1/4096 fixed point (vftoi12), replicated into halfword lanes.
3. The blend. Per vertex and axis, in the EE's 16-bit SIMD:
   • the target's difference from the base (psubh, wrapping);
   • times the weight, summed in 32 bits over the targets (pmaddh through HI/LO);
   • shifted down 12 (psraw, a floor);
   • added back to the base with 16-bit saturation (paddsh).

Model::morph in piney-data does the same.

• ModelDraw gained a morph list (target model, weight).
• The stream draw fills it from the node's modifier, its targets resolved to models of the drawn model's file.
• The GPU renderer and the CPU GS model both draw the blended positions.

The result

At frame 822 the four ribbons are no longer straight bands. They are thin tendrils winding around the figure, and by frame 850 they have moved.

Checked

• The arithmetic. morph_blends_as_the_ee_does covers the floor of the shift, a target at another scale, and the 16-bit wrap and saturation: -32000 toward 32000 at weight 1 wraps to -1536 and saturates at -32768.
• The stream. ribbons_are_morphed: at stream 2's frame 822 exactly four model draws carry two targets whose weights sum to 1, and each blend moves the base positions.
• The rest. The workspace's tests pass, and clippy and fmt are clean.