The Allegro Wiki is migrating to github at

Vector graphic objects

From Allegro Wiki
Revision as of 01:13, May 22, 2009 by Matt Smith (talk | contribs) (type definition of AREA struct)
Jump to: navigation, search

Vector Graphic Objects

A VectorGraphics Subject These are the datatypes used in the prototype Vector Render API.

fig 1

Vector shapes are represented in memory by a series of vertices, connected by lines. LINE fragments are joined into PATHs. Where lines intersect, a new PATH is started. Filled AREAs are defined by a list of PATHs. They are defined in order (clockwise).

A small example of a 2d vector object engine in C

type definition of SHAPE struct

<highlightSyntax language="cpp">typedef struct SHAPE {

  V2D_f * verts;    /* list of vertices, including invisible control points */
  LINE * lines;     /* each line segment has 4 control points, 2 are unused for
                       straight segments */
  PATH * paths;     /* each path is a list of line segments */
  AREA * areas;     /* areas are bounded by list of paths (indexed from paths list) */   



type definition of LINE struct

<highlightSyntax language="cpp">typedef struct LINE {

  int p1,p2;            /* start and end points (index to vertex list) */
  int p3,p4;            /* bezier control points */
  float thickness;      
  int color;



type definition of PATH struct

<highlightSyntax language="cpp">typedef struct PATH {

  int p1,p2;            /* start and end verts */
  int n_seg;            /* number of segments in line */
  int segs[];           /* list of indices to shape->lines */ 



type definition of AREA struct

<highlightSyntax language="cpp">typedef struct AREA {

  int n_paths;           /* number of segments in line */
  int paths[];           /* list of indices to shape->paths, with direction bit */ 

                               FILLTYPE_RADIALGRADIENT, FILLTYPE_TEXTURED */ 
  GRADIENT * gradient;   /* specifies gradient table when FILLTYPE_LINEARGRADIENT or FILLTYPE_RADIALGRADIENT
                            are used */
  AL_BITMAP * bmp;       /* specifies bitmap to use as texture when FILLTYPE_TEXTURED is used*/
  // int gl_tex;         /* only used in A4 as above*/   
  float fill_ox,fill_oy;  /* origin of fill co-ords */     
  float fill_ux,fill_uy;  /* u axis, relative to ox,oy */   
  float fill_vx,fill_vy;  /* v axis */