Master of Puppets

Location

include/mop/export/obj_export.h    — Wavefront OBJ
include/mop/export/scene_export.h  — JSON scene description
include/mop/export/image_export.h  — PNG framebuffer / buffer
src/export/obj_export.c
src/export/scene_export.c
src/export/image_export.c

All export functions return 0 on success and -1 on failure.

OBJ Export

mop_export_obj_mesh

int mop_export_obj_mesh(const MopMesh *mesh, const MopViewport *vp,
                        const char *path);

Write a single mesh to a Wavefront OBJ file. Vertex / index data is read via the zero-copy query API (see Query). Local positions are written as-is — world transform is not baked for single-mesh export.

mop_export_obj_scene

int mop_export_obj_scene(const MopViewport *vp, const char *path);

Write every active mesh in the viewport to a single OBJ file. Positions are baked by the world transform; normals are transformed by the upper-3×3 of the world matrix (approximate for non-uniform scale). Each mesh is emitted as a named object group (o object_<id>); index bases auto-increment across meshes.

Scene JSON Export

mop_export_scene_json

int mop_export_scene_json(const MopViewport *vp, const char *path);

Human-readable JSON snapshot of scene state for debug tooling, regression diffs, or round-tripping to external editors. Contents:

Camera: eye, target, up, fov (degrees), near, far
Lights: type, position / direction, color (linear), intensity
Objects: per-mesh object_id, TRS position / rotation / scale, base_color, metallic, roughness

Not included: vertex / index data (use OBJ or .mop), textures, IBL state, post-process flags.

Implemented with snprintf — no JSON library dependency.

PNG Export

mop_export_png

int mop_export_png(MopViewport *vp, const char *path);

Read the current framebuffer via mop_viewport_read_color and write it as PNG. Call after mop_viewport_render. Pixel format is RGBA8.

mop_export_png_buffer

int mop_export_png_buffer(const uint8_t *rgba, int width, int height,
                          const char *path);

Write an application-owned RGBA8 buffer as PNG. Stride is width * 4. Useful for saving composited / annotated images without routing through a viewport.

Both variants use stb_image_write internally.

Usage

/* Render one frame and save as PNG. */
mop_viewport_render(vp);
mop_export_png(vp, "frame.png");

/* Export entire scene (with baked transforms) to OBJ. */
mop_export_obj_scene(vp, "scene.obj");

/* Snapshot scene state to JSON for diff / QA. */
mop_export_scene_json(vp, "scene.json");

/* Save a composited buffer you built by hand. */
mop_export_png_buffer(my_rgba, w, h, "annotated.png");

22 APR 2026

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