Location

src/core/
  viewport.c            — Viewport lifecycle, scene, rendering, passes
  viewport_internal.h   — Internal struct definitions
  light.c               — Light management and light indicators
  display.c             — Display settings
  overlay.c             — Overlay system
  overlay_builtin.c     — Built-in overlay implementations
  vertex_format.c       — Flexible vertex format
  subsystem.c           — Subsystem vtable dispatch

Internal Structures

MopViewport

struct MopViewport {
    const MopRhiBackend *rhi;          /* Backend function table        */
    MopRhiDevice        *device;       /* Backend device instance       */
    MopRhiFramebuffer   *framebuffer;  /* Color+depth+ID targets        */
    MopBackendType       backend_type; /* Active backend enum value     */

    int width, height;                 /* Framebuffer dimensions        */
    MopColor      clear_color;         /* Per-frame clear value         */
    MopRenderMode render_mode;         /* Solid or wireframe            */
    MopShadingMode shading_mode;       /* Flat or smooth                */

    /* Camera */
    MopOrbitCamera camera;             /* Orbit camera state            */
    MopVec3 cam_eye, cam_target, cam_up;
    float   cam_fov_radians, cam_near, cam_far;
    MopMat4 view_matrix, projection_matrix;

    /* Scene — flat array with active flags */
    struct MopMesh meshes[MOP_MAX_MESHES];
    uint32_t       mesh_count;

    /* Lights */
    MopLight  lights[MOP_MAX_LIGHTS];  /* Up to 8 lights               */
    uint32_t  light_count;
    MopMesh  *light_indicators[MOP_MAX_LIGHTS]; /* Visual indicators   */

    /* Interaction */
    MopGizmo        *gizmo;            /* TRS manipulation gizmo       */
    uint32_t         selected_id;      /* Currently selected object ID  */
    MopInteractState interact_state;   /* State machine (idle, orbit..) */
    MopGizmoAxis     drag_axis;        /* Active drag axis              */
    float click_start_x, click_start_y;

    /* Event queue */
    MopEvent events[MOP_MAX_EVENTS];
    int      event_head, event_tail;

    /* Overlays */
    MopOverlayEntry overlays[MOP_MAX_OVERLAYS];
    uint32_t        overlay_count;

    /* Display settings */
    MopDisplaySettings display;

    /* Post-processing */
    uint32_t post_effects;             /* Bitmask of MopPostEffect      */

    /* Undo/redo stacks */
    /* ... */

    /* Subsystems (particles, water) */
    /* ... */

    /* Timing */
    float time, last_time;
};

MopMesh (internal)

struct MopMesh {
    MopRhiBuffer *vertex_buffer;
    MopRhiBuffer *index_buffer;
    uint32_t      vertex_count, index_count;
    uint32_t      object_id;
    MopMat4       transform;
    MopVec3       position, rotation, scale_val;
    bool          use_trs;
    MopColor      base_color;
    float         opacity;
    MopBlendMode  blend_mode;
    MopMaterial   material;
    bool          has_material;
    MopVertexFormat vertex_format;
    MopMesh      *parent;
    bool          active;
};

Scene Management

Meshes are stored in a flat array of MOP_MAX_MESHES (4096) entries. Adding a mesh scans for an inactive slot or appends. Removing a mesh marks it inactive and destroys its RHI buffers. The viewport destroy function walks the entire array.

Rendering Orchestration

mop_viewport_render orchestrates multiple passes:

1. Frame begin — clear color, depth, and object ID buffers
2. Light indicator update — create/destroy/reposition indicator meshes for active lights
3. Gizmo update — recompute handle positions and screen-space scale
4. Pass: scene — draw all active meshes with object_id < 0xFFFE0000 (depth test on, backface cull on)
5. Pass: gizmo + indicators — draw gizmo handles (object_id >= 0xFFFF0000) and light indicators (object_id >= 0xFFFE0000) without depth test or backface cull
6. Pass: overlays — wireframe, normals, bounds, selection highlight, custom overlays
7. Post-processing — gamma, tonemapping, vignette, fog
8. Frame end — finalize and make framebuffer readable

Object ID Ranges