forge-pipeline-morph-animations

Add morph target animation support to an SDL GPU project that already uses `forge_scene.h`. This skill covers loading `.fmesh` files with morph data, evaluating morph weight animation from `.fanim` channels, CPU-blending per-vertex deltas, and uploading to GPU storage buffers for vertex shader displacement. ## Prerequisites - `forge_scene.h` with `FORGE_SCENE_MODEL_SUPPORT` enabled - `forge_pipeline.h` for `.fmesh` and `.fanim` loading - Pipeline-processed assets with `FLAG_MORPHS` set in `.fmesh` - Compiled morph shaders (`scene_morph.vert.hlsl`, `scene_morph_shadow.vert.hlsl`) ## Asset processing Process glTF models with morph targets using the pipeline tools: ```bash forge_mesh_tool model.gltf model.fmesh --verbose forge_scene_tool model.gltf model.fscene --verbose forge_anim_tool model.gltf model.fanim --verbose ``` The mesh tool detects morph targets and sets `FLAG_MORPHS` in the `.fmesh` header. It also disables vertex deduplication (morph deltas reference original vertex indices). The anim tool preserves `MORPH_WEIGHTS` channels (`target_path = 3`) with variable component counts. ## Loading a morph model ```c #define FORGE_SCENE_MODEL_SUPPORT #define FORGE_SCENE_IMPLEMENTATION #include "scene/forge_scene.h" ForgeSceneMorphModel morph_model; /* fmat_path may be NULL if no materials; fanim_path may be NULL for manual weights */ if (!forge_scene_load_morph_model(&scene, &morph_model, fscene_path, fmesh_path, fmat_path, fanim_path, base_dir)) { SDL_Log("Failed to load morph model"); return SDL_APP_FAILURE; } ``` ## Updating morph animation each frame ```c /* After forge_scene_begin_frame(): */ morph_model.anim_speed = speed_slider_value; /* Toggle manual_weights to override animation with direct control */ if (morph_model.manual_weights) { morph_model.morph_weights[0] = slider_w0; morph_model.morph_weights[1] = slider_w1; } forge_scene_update_morph_animation(&scene, &morph_model, dt); ``` `forge_scene_update_morph_animation` does three things: 1. Evaluates morph weight channels from `.fanim` (unless `manual_weights` is set) 2. CPU-blends position and normal deltas: `blended[v] += weight * delta[v]` 3. Uploads blended deltas to GPU storage buffers via persistent transfer buffer ## Drawing ```c mat4 placement = mat4_multiply( mat4_translate(vec3_create(x, y, z)), mat4_scale_uniform(scale)); /* Shadow pass */ forge_scene_begin_shadow_pass(&scene); forge_scene_draw_morph_model_shadows(&scene, &morph_model, placement); forge_scene_end_shadow_pass(&scene); /* Main pass */ forge_scene_begin_main_pass(&scene); forge_scene_draw_grid(&scene); forge_scene_draw_morph_model(&scene, &morph_model, placement); forge_scene_end_main_pass(&scene); ``` ## Cleanup ```c forge_scene_free_morph_model(&scene, &morph_model); ``` ## Shader approach The morph vertex shader uses the standard 48-byte vertex layout (same as `scene_model.vert.hlsl`) plus two `StructuredBuffer<float4>` for position and normal deltas, indexed by `SV_VertexID`. The float4 type ensures a consistent 16-byte stride across SPIRV and DXIL backends: ```hlsl StructuredBuffer<float4> morph_pos_deltas : register(t0, space0); StructuredBuffer<float4> morph_nrm_deltas : register(t1, space0); float3 morphed_pos = input.position + morph_pos_deltas[input.vertex_id].xyz; float3 morphed_nrm = normalize(input.normal + morph_nrm_deltas[input.vertex_id].xyz); ``` The shadow variant uses only position deltas (1 storage buffer). ## Reference - [GPU Lesson 44 — Pipeline Morph Target Animations](../../../lessons/gpu/44-pipeline-morph-animations/) - [Asset Lesson 13 — Morph Targets](../../../lessons/assets/13-morph-targets/) - [GPU Lesson 43 — Pipeline Skinned Animations](../../../lessons/gpu/43-pipeline-skinned-animations/) — same CPU-compute + GPU-apply pattern