The GGI2D interface
 Thomas Tanner, [email protected]
 $Date: 1998/02/17 10:53:35 $

 This document describes the LibGGI2D, the extension library to LibGGI
 providing common 2D graphics primitives.

 1.  Introduction

 This is (as of 22-Jan-98) an API proposal! This is not implemented
 yet!


 While the LibGGI is meant to be very low-level and near to the
 graphics board, this library contains more



 2.  Functions to manipulate the current graphics context

 2.1.  General


 The default values of an visual are:

 o  arc mode: GGI_ARC_PIE

 o  poly mode: GGI_POLY_ALTERNATE

 o  line stipple: normal line

 o  antialiasing: no

 o  clipping rectangle:((0,0),(width,height))

 o  drawcolor: white

 o  fillcolor: black

 o  texture: none

 o  operator: GGI_SET

 o  alpha: 100%



 2.1.1.  void ggiResetVisual(ggi_dc dc);

 Reset the visual to the default values (as listed above).


 2.2.  Clipping

 2.2.1.  void ggiSetClip(ggi_visual vis, int x1, int y1, int x2, int
 y2);

 Set the clipping rectangle to the intersection of ((x1,y1),(x2,y2))
 and the current clipping rectangle.  A pixel (x,y) lies inside the
 clipping rectangle if (x >= x1 && y >= y2 && x < x2 && y < y2).
 ggiSetClip(dc, x, y, x, y) disables all drawing.





 2.2.2.  void ggiResetClip(ggi_visual vis);

 Reset the clipping rectangle to default values.


 2.2.3.  ggi_bool ggiPointVisible(ggi_visual vis, int x, int y);

 Returns true if the point (x,y) lies inside the clipping rectangle.


 2.2.4.  ggi_bool ggiRectVisible(ggi_visual vis, int x1, int y1, int
 x2, int y2);

 Returns true if the rectangle ((x1,y1),(x2,y2)) intersects the
 clipping rectangle.

 2.3.  Drawing modes

 2.3.1.  void ggiSetArcMode(ggi_visual vis, ggi_arcmode mode);

 2.3.2.  ggi_arcmode ggiGetArcMode(ggi_visual vis);

 Set/Get the current arc mode:

  typedef enum {
  GGI_ARC_PIE,
  GGI_ARC_CHORD
  } ggi_arcmode;




 2.3.3.  void ggiSetPolyMode(ggi_visual vis, ggi_polymode mode);

 2.3.4.  ggi_polymode ggiGetPolyMode(ggi_visual vis);

 Set/Get the current polygon mode:

  typedef enum {
  GGI_POLY_ALTERNATE,
  /* alternate rule */
  GGI_POLY_WINDING
  /* winding rule */
  } ggi_polymode;




 2.3.5.  void ggiSetLineStipple(ggi_visual vis, uint stipple, uint
 count);

 2.3.6.  void ggiGetLineStipple(ggi_visual vis, uint *stipple, uint
 *count);

 Set/Get the current line stipple.

 2.3.7.  void ggiSetAntialias(ggi_visual vis, ggi_bool antialias);

 2.3.8.  ggi_bool ggiGetAntialias(ggi_visual vis);

 Set/Get the antialiasing mode.

 2.4.  Color and texture



 2.4.1.  void ggiSetDrawColor(ggi_visual vis, ggi_col color);

 2.4.2.  ggi_col ggiGetDrawColor(ggi_visual vis);

 Set/Get the current drawing color.


 2.4.3.  void ggiSetFillColor(ggi_visual vis, ggi_col color);

 2.4.4.  ggi_col ggiGetFillColor(ggi_visual vis);

 Set/Get the current filling color.


 2.4.5.  void ggiSetFillTexture(ggi_visual vis, int refx, int refy,
 ggi_visual texture);

 Set the texture and the reference point (refx,refy).  The color of a
 drawn pixel at (x,y) is now the texel at (abs(refx-x) mod
 texture.width, abs(refy-y) mod texture.height).


 2.4.6.  ggi_visual ggiGetFillTexture(ggi_visual vis, int *refx, int
 *refy);

 Get the current texture and reference point.  Returns NULL and (0,0)
 if no texture is set.

 2.5.  Drawing style

 2.5.1.  void ggiSetOperator(ggi_visual vis, ggi_operator operator);

 2.5.2.  ggi_operator ggiGetOperator(ggi_visual vis);

 Set/Get the current operator.

  typedef enum {
  GGI_NOOP, /* dest = dest */
  GGI_INVERT, /* dest = ~dest */
  GGI_SET, /* dest = src */
  GGI_SET_INVERTED, /* dest = ~src */
  GGI_AND, /* dest = (dest & src) */
  GGI_NAND, /* dest = ~(dest & src) */
  GGI_AND_REVERSE, /* dest = ~dest & src */
  GGI_AND_INVERTED, /* dest = dest & ~src */
  GGI_OR, /* dest = (dest | src) */
  GGI_NOR, /* dest = ~(dest | src) */
  GGI_OR_REVERSE, /* dest = ~dest & src */
  GGI_OR_INVERTED, /* dest = dest & ~src */
  GGI_XOR, /* dest = (dest ^ src) */
  GGI_EQUIV, /* dest = ~(dest ^ src) */
  GGI_ADD, /* dest = dest + src */
  GGI_SUB /* dest = dest - src */
  } ggi_operator;





 2.5.3.  void ggiSetAlpha(ggi_visual vis, ggi_alpha alpha);

 2.5.4.  ggi_alpha ggiGetAlpha(ggi_visual vis);

 Set/Get the current alpha value.


 3.  Drawing functions


 3.1.  Pixels

 3.1.1.  void ggiGetPixel(ggi_visual vis, int x, int y, ggi_col *color)

 Get the color of the pixel at (x,y).  Returns 0 if the point lies
 outside the clipping rectangle.


 3.1.2.  void ggiPutPixel(ggi_visual vis, int x, int y, ggi_col color);

 3.1.3.  void ggiPutPixelA(ggi_visual vis, int x, int y, ggi_col color,
 ggi_alpha alpha);

 3.1.4.  void ggiDrawPixel(ggi_visual vis, int x, int y);

 3.1.5.  void ggiDrawPixelA(ggi_visual vis, int x, int y, ggi_alpha
 alpha);

 Draw a pixel at (x,y).


 3.1.6.  void ggiDrawPixels(ggi_visual vis, ggi_coord coords[], uint
 count);

 Draw several pixels.

 3.2.  Lines

 3.2.1.  void ggiHLine(ggi_visual vis, int x1, int x2, int y);

 Draw a horizontal line from (x1,y) to (x2,y).  Note: This line is not
 stippled!


 3.2.2.  void ggiVLine(ggi_visual vis, int x, int y1, int y2);

 Draw a vertical line from (x,y1) to (x,y2).  Note: This line is not
 stippled!


 3.2.3.  void ggiDrawRect(ggi_visual vis, int x1, int y1, int x2, int
 y2);

 3.2.4.  void ggiFillRect(ggi_visual vis, int x1, int y1, int x2, int
 y2);

 Draw/Fill the rectangle ((x1,y1),(x2,y2)).


 3.2.5.  void ggiLine(ggi_visual vis, int x1, int y1, int x2, int y2);

 3.2.6.  void ggiLinef(ggi_visual vis, ggi_float x1, ggi_float y1,
 ggi_float x2, ggi_float y2);

 Draw a line from (x1,y1) to (x2,y2).


 3.2.7.  void ggiDrawLines(ggi_visual vis, ggi_line lines[], uint
 count);

 Draw several lines.


 3.3.  Circles and curves

 3.3.1.  void ggiDrawCircle(ggi_visual vis, int x, int y, uint r);

 3.3.2.  void ggiFillCircle(ggi_visual vis, int x, int y, uint r);


 Draw/Fill a circle with radius r around (x,y).


 3.3.3.  void ggiDrawEllipse(ggi_visual vis, int x, int y, uint rx,
 uint ry);

 3.3.4.  void ggiFillEllipse(ggi_visual vis, int x, int y, uint rx,
 uint ry);


 Draw/Fill an ellipse with radius (rx,ry) around (x,y).


 3.3.5.  void ggiDrawArc(ggi_visual vis, int x, int y, uint rx, uint
 ry, ggi_float start, ggi_float end, ggi_bool close);


 Draw an arc with radius (rx,ry) around (x,y) between "start" and "end"
 (degree).  If close is GGI_TRUE, the arc will be closed (using
 arcmode).


 3.3.6.  void ggiFillArc(ggi_visual vis, int x, int y, uint rx, uint
 ry, ggi_float start, ggi_float end);


 Fill an arc with radius (rx,ry) around (x,y) between "start" and "end"
 (degree).


 3.3.7.  void ggiBezier(ggi_visual vis, int x1, int y1, int x2, int y2,
 int x3, int y3, int x4, int y4);


 Draw a bezier curve.


 3.4.  Polygons

 3.4.1.  void ggiTrapezoid(ggi_visual vis, int xl1, int xr1, int y1,
 int xl2, int xr2, int y2);


 Fill a trapezoid.


 3.4.2.  void ggiTriangle(ggi_visual vis, int x1, int y1, int x2, int
 y2, int x3, int y3);


 Fill a triangle.


 3.4.3.  void ggiDrawPoly(ggi_visual vis, ggi_coord coords[], uint
 count);




 3.4.4.  void ggiFillPoly(ggi_visual vis, ggi_coord coords[], uint
 count);


 Draw/Fill a polygon.


 3.4.5.  void ggiFillPolys(ggi_visual vis, ggi_coord coords[], uint
 counts[], uint count);


 Fill several (overlapping) polygons.


 3.5.  Scrolling/Blitting functions



 3.5.1.  void ggiScroll( ggi_visual vis, int dx, int dy, int sx, int
 sy, int width, int height);


 Copy the rectangular area ((sx,sy),(sx+width,sy+height)) to (dx,dy).

 3.5.2.  void ggiBlit(ggi_visual vis, int dx, int dy, ggi_visual src,
 int sx, int sy, int width, int height);

 3.5.3.  void ggiStretchBlit(ggi_visual dest, int dx, int dy, int
 dwidth, int dheight, ggi_visual src, int sx, int sy, int swidth, int
 sheight);


 Copy the rectangular area ((sx,sy),(sx+width,sy+height)) from "src" to
 (dx,dy).  ggiStretchBlit() can scale the image.

 3.5.4.  void ggiBlitTrans(ggi_visual dest, int dx, int dy, ggi_visual
 src, int sx, int sy, int width, int height, ggi_col transcol);

 3.5.5.  void ggiStretchBlitTrans(ggi_visual dest, int dx, int dy, int
 dwidth, int dheight,ggi_visual src, int sx, int sy, int swidth, int
 sheight,ggi_col transcol);


 Copy the rectangular area ((sx,sy),(sx+width,sy+height)) from "src" to
 (dx,dy). Pixels with color "transcol" are not drawn.
 ggiStretchBlitTrans() can scale the image.


 3.5.6.  void ggiBlitOp(ggi_visual dest, int dx, int dy, ggi_visual
 src1, ggi_visual src2, int sx, int sy, int width, int height,
 ggi_operator op);

 3.5.7.  void ggiStretchBlitOp(ggi_visual dest, int dx, int dy, int
 dwidth, int dheight, ggi_visual src1, ggi_visual src2, int sx, int sy,
 int swidth, int sheight, ggi_operator op);


 Apply the operator "op" to all pixels of the rectangular areas
 ((sx,sy),(sx+width,sy+height)) of "src1" and "src2" and draw them only
 if the result is not 0.  ggiStretchBlitOp() can scale the image.

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