Types:

GE_RGBA;

typedef struct {
    float r, g, b, a;
} GE_RGBA;

typedef struct {
    int32 Left;
    int32 Right;
    int32 Top;
    int32 Bottom;
} GE_Rect;

typedef GE_Rect geRect;

geFloatRect;

typedef struct {
    geFloat MinX,MaxX;
    geFloat MinY,MaxY;
} geFloatRect;

typedef struct {
    float X, Y, Z;         // 3d vertex
    float u, v;              // Uv's
    float r, g, b, a;       // color
} GE_LVertex;

This structure stores a Lit Vertex.
 

typedef struct {
    float x, y, z;            // screen points
    float u, v;               // Uv's
    float r, g, b, a;        // color
} GE_TLVertex;

This structure stores a Transformed Lit Vertex.

Questions:
    What is meant by Transformed?  This seems to be the same as GE_LVertex except the x,y,z here are labeled screen points. What are screen point?  Is this in screen coordinate space?

Macros:

Model flags (geWorld_ModelSetFlags)

#define GE_MODEL_RENDER_NORMAL   (1<<0)  // Render in normal views
#define GE_MODEL_RENDER_MIRRORS   (1<<1)  // Render in mirror views
#define GE_MODEL_RENDER_ALWAYS   (1<<2)  // Render always, skipping all visibility tests
#define GE_MODEL_COLLIDE    (1<<3)  // Collide when calling geWorld_Collision