4 Draw, Clear, and Flip Operations

▼ |  | Graphics: Legacy Library

1 | Basic Commands
2 | Position Operations
3 | Color Operations
4 | Draw, Clear, and Flip Operations
5 | World Operations
6 | Miscellaneous Operations
7 | An Example
8 | A More Complicated Example
9 | Protecting Graphics Operations
10 | Mouse Operations
11 | Keyboard Operations
12 | Flushing
13 | Graphics Library as a Unit

► | 4 | Draw, Clear, and Flip Operations

4.1 | Viewports
4.2 | Pixels
4.3 | Lines
4.4 | Rectangles
4.5 | Ellipses
4.6 | Polygons
4.7 | Strings
4.8 | Pixmaps

On this page:

4.1`` Viewports
draw-viewport
clear-viewport
flip-viewport
copy-viewport
4.2`` Pixels
draw-pixel
clear-pixel
flip-pixel
4.3`` Lines
draw-line
clear-line
flip-line
4.4`` Rectangles
draw-rectangle
clear-rectangle
flip-rectangle
draw-solid-rectangle
clear-solid-rectangle
flip-solid-rectangle
4.5`` Ellipses
draw-ellipse
clear-ellipse
flip-ellipse
draw-solid-ellipse
clear-solid-ellipse
flip-solid-ellipse
4.6`` Polygons
draw-polygon
clear-polygon
flip-polygon
draw-solid-polygon
clear-solid-polygon
flip-solid-polygon
4.7`` Strings
draw-string
clear-string
flip-string
4.8`` Pixmaps
draw-pixmap-posn
draw-pixmap
save-pixmap

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### 4`` Draw, Clear, and Flip Operations

The following are the basic graphics operations for drawing to a viewport. Each function takes a viewport as its argument and returns a function operating within that viewport. Further arguments, if any, are curried. For example, (draw-line viewport) returns a function, that can then be applied to the proper arguments to draw a line in the viewport corresponding to viewport descriptor viewport.

In general, draw- functions make pixels black or colored, clear- functions make them white, and flip- commands invert pixels (which makes black white, white black, and is otherwise ill-defined).

#### 4.1`` Viewports

> procedure ((draw-viewport viewport) [color]) → void?
> viewport : viewport?
> | color |  | : |  |
> (or/c (integer-in 0 299)
> string?
> rgb?)
> |  | = |  | "black"

Colors the entire contents of viewport with color.

> procedure ((clear-viewport viewport)) → void?
> viewport : viewport?

Whitens the entire contents of viewport.

> procedure ((flip-viewport viewport)) → void?
> viewport : viewport?

Inverts the entire contents of viewport.

> procedure (copy-viewport source dest) → void?
> source : viewport?
> dest : viewport?

Copies the content of source into dest.

#### 4.2`` Pixels

> procedure ((draw-pixel viewport) p [color]) → void?
> viewport : viewport?
> p : posn?
> | color |  | : |  |
> (or/c (integer-in 0 299)
> string?
> rgb?)
> |  | = |  | "black"

Colors the pixel in viewport at p.

> procedure ((clear-pixel viewport) p) → void?
> viewport : viewport?
> p : posn?

Whitens the pixel in viewport at p.

> procedure ((flip-pixel viewport) p) → void?
> viewport : viewport?
> p : posn?

Inverts the pixel in viewport at p.

#### 4.3`` Lines

> procedure ((draw-line viewport) p1 p2 [color]) → void?
> viewport : viewport?
> p1 : posn?
> p2 : posn?
> | color |  | : |  |
> (or/c (integer-in 0 299)
> string?
> rgb?)
> |  | = |  | "black"

Draws a line in viewport connecting positions p1 and p2.

> procedure ((clear-line viewport) p1 p2) → void?
> viewport : viewport?
> p1 : posn?
> p2 : posn?

Whitens a line in viewport connecting positions p1 and p2.

> procedure ((flip-line viewport) p1 p2) → void?
> viewport : viewport?
> p1 : posn?
> p2 : posn?

Inverts a line in viewport connecting positions p1 and p2.

#### 4.4`` Rectangles

> > procedure
> > ((draw-rectangle |  | viewport) |  |  |  |
> > |  | p |  |  |  |
> > |  | width |  |  |  |
> > |  | height |  |  |  |
> > | [ | color]) |  | → |  | void?
> viewport : viewport?
> p : posn?
> width : (and/c real? (not/c negative?))
> height : (and/c real? (not/c negative?))
> | color |  | : |  |
> (or/c (integer-in 0 299)
> string?
> rgb?)
> |  | = |  | "black"

Draws a rectangle border in the viewport with the top-left of the rectangle at the position p and with sides width across and height tall.

> procedure ((clear-rectangle viewport) p width height) → void?
> viewport : viewport?
> p : posn?
> width : (and/c real? (not/c negative?))
> height : (and/c real? (not/c negative?))

Whitens a rectangle border in the viewport, analogous to draw-rectangle.

> procedure ((flip-rectangle viewport) p width height) → void?
> viewport : viewport?
> p : posn?
> width : (and/c real? (not/c negative?))
> height : (and/c real? (not/c negative?))

Inverts a rectangle border in the viewport, analogous to draw-rectangle.

> > procedure
> > ((draw-solid-rectangle |  | viewport) |  |  |  |
> > |  | p |  |  |  |
> > |  | width |  |  |  |
> > |  | height |  |  |  |
> > | [ | color]) |  | → |  | void?
> viewport : viewport?
> p : posn?
> width : (and/c real? (not/c negative?))
> height : (and/c real? (not/c negative?))
> | color |  | : |  |
> (or/c (integer-in 0 299)
> string?
> rgb?)
> |  | = |  | "black"

Draws a solid rectangle in the viewport with the top-left of the rectangle at the position p and with sides width across and height tall.

> > procedure
> > ((clear-solid-rectangle |  | viewport) |  |  |  |
> > |  | p |  |  |  |
> > |  | width |  |  |  |
> > |  | height) |  | → |  | void?
> viewport : viewport?
> p : posn?
> width : (and/c real? (not/c negative?))
> height : (and/c real? (not/c negative?))

Whitens a rectangle border in the viewport, analogous to draw-solid-rectangle.

> > procedure
> > ((flip-solid-rectangle |  | viewport) |  |  |  |
> > |  | p |  |  |  |
> > |  | width |  |  |  |
> > |  | height) |  | → |  | void?
> viewport : viewport?
> p : posn?
> width : (and/c real? (not/c negative?))
> height : (and/c real? (not/c negative?))

Inverts a rectangle border in the viewport, analogous to draw-solid-rectangle.

#### 4.5`` Ellipses

> procedure ((draw-ellipse viewport) p width height [color]) → void?
> viewport : viewport?
> p : posn?
> width : (and/c real? (not/c negative?))
> height : (and/c real? (not/c negative?))
> | color |  | : |  |
> (or/c (integer-in 0 299)
> string?
> rgb?)
> |  | = |  | "black"

Draws a ellipse border in the viewport. The ellipse is inscribed with a rectangle whose top-left is at position p and with sides width across and height tall.

> procedure ((clear-ellipse viewport) p width height) → void?
> viewport : viewport?
> p : posn?
> width : (and/c real? (not/c negative?))
> height : (and/c real? (not/c negative?))

Whitens a ellipse border in the viewport, analogous to draw-ellipse.

> procedure ((flip-ellipse viewport) p width height) → void?
> viewport : viewport?
> p : posn?
> width : (and/c real? (not/c negative?))
> height : (and/c real? (not/c negative?))

Inverts a ellipse border in the viewport, analogous to draw-ellipse.

> > procedure
> > ((draw-solid-ellipse |  | viewport) |  |  |  |
> > |  | p |  |  |  |
> > |  | width |  |  |  |
> > |  | height |  |  |  |
> > | [ | color]) |  | → |  | void?
> viewport : viewport?
> p : posn?
> width : (and/c real? (not/c negative?))
> height : (and/c real? (not/c negative?))
> | color |  | : |  |
> (or/c (integer-in 0 299)
> string?
> rgb?)
> |  | = |  | "black"

Draws a solid ellipse in the viewport. The ellipse is inscribed with a rectangle whose top-left is at position p and with sides width across and height tall.

> > procedure
> > ((clear-solid-ellipse |  | viewport) |  |  |  |
> > |  | p |  |  |  |
> > |  | width |  |  |  |
> > |  | height) |  | → |  | void?
> viewport : viewport?
> p : posn?
> width : (and/c real? (not/c negative?))
> height : (and/c real? (not/c negative?))

Whitens a ellipse border in the viewport, analogous to draw-solid-ellipse.

> > procedure
> > ((flip-solid-ellipse |  | viewport) |  |  |  |
> > |  | p |  |  |  |
> > |  | width |  |  |  |
> > |  | height) |  | → |  | void?
> viewport : viewport?
> p : posn?
> width : (and/c real? (not/c negative?))
> height : (and/c real? (not/c negative?))

Inverts a ellipse border in the viewport, analogous to draw-solid-ellipse.

#### 4.6`` Polygons

> procedure ((draw-polygon viewport) points offset [color]) → void?
> viewport : viewport?
> points : (listof posn?)
> offset : posn?
> | color |  | : |  |
> (or/c (integer-in 0 299)
> string?
> rgb?)
> |  | = |  | "black"

Draws a polygon border in viewport using points for the polygon vertices and offset as an offset added to all points.

> procedure ((clear-polygon viewport) points offset) → void?
> viewport : viewport?
> points : (listof posn?)
> offset : posn?

Whitens a polygon border in viewport, analogous to draw-polygon.

> procedure ((flip-polygon viewport) points offset) → void?
> viewport : viewport?
> points : (listof posn?)
> offset : posn?

Inverts a polygon border in viewport, analogous to draw-polygon.

> > procedure
> > ((draw-solid-polygon |  | viewport) |  |  |  |
> > |  | points |  |  |  |
> > |  | offset |  |  |  |
> > | [ | color]) |  | → |  | void?
> viewport : viewport?
> points : (listof posn?)
> offset : posn?
> | color |  | : |  |
> (or/c (integer-in 0 299)
> string?
> rgb?)
> |  | = |  | "black"

Draws a solid polygon in viewport using points for the polygon vertices and offset as an offset added to all points.

> > procedure
> > ((clear-solid-polygon |  | viewport) |  |  |  |
> > |  | points |  |  |  |
> > |  | offset) |  | → |  | void?
> viewport : viewport?
> points : (listof posn?)
> offset : posn?

Whitens a polygon border in viewport, analogous to draw-solid-polygon.

> > procedure
> > ((flip-solid-polygon |  | viewport) |  |  |  |
> > |  | points |  |  |  |
> > |  | offset) |  | → |  | void?
> viewport : viewport?
> points : (listof posn?)
> offset : posn?

Inverts a polygon border in viewport, analogous to draw-solid-polygon.

#### 4.7`` Strings

> procedure ((draw-string viewport) p str [color]) → void?
> viewport : viewport?
> p : posn?
> str : string?
> | color |  | : |  |
> (or/c (integer-in 0 299)
> string?
> rgb?)
> |  | = |  | "black"

Draws a string at a specified location in the viewport. The lower left of the string begins at p.

> procedure ((clear-string viewport) p str) → void?
> viewport : viewport?
> p : posn?
> str : string?

Whitens a string at a specified location in the viewport. The lower left of the string begins at p.

> procedure ((flip-string viewport) p str) → void?
> viewport : viewport?
> p : posn?
> str : string?

Inverts a string at a specified location in the viewport. The lower left of the string begins at p.

#### 4.8`` Pixmaps

> > procedure
> > (((draw-pixmap-posn |  | file |  |  |  |
> > | [ | type])) |  |  |  |
> > |  | viewport) |  |  |  |
> > |  | p |  |  |  |
> > | [ | color]) |  | → |  | void?
> file : path-string?
> | type |  | : |  |
> (one-of/c 'unknown 'unknown/mask
> 'gif 'gif/mask 'jpeg 'png 'png/mask
> 'xbm 'xpm 'bmp)
> |  |  | = |  | 'unknown/mask
> viewport : viewport?
> p : posn?
> | color |  | : |  |
> (or/c (integer-in 0 299)
> string?
> rgb?)
> |  | = |  | "black"

Draws a pixmap into viewport with its upper left corner at position p. If type is 'unknown or 'unknown/mask, then the content of the file is examined to determine the type. The 'gif/mask, 'png/mask, and 'unknown/mask types draw the bitmap with a transparent background if filename refers to a GIF/PNG file with a transparent background.

The argument color is only used when the loaded pixmap is monochrome. In that case, the color is used instead of black in the drawn image.

> procedure ((draw-pixmap viewport) file p [color]) → void?
> viewport : viewport?
> file : path-string?
> p : posn?
> | color |  | : |  |
> (or/c (integer-in 0 299)
> string?
> rgb?)
> |  | = |  | "black"

Equivalent to (((draw-pixmap-posn file) viewport) p color).

> procedure ((save-pixmap viewport) file [type]) → void?
> viewport : viewport?
> file : path-string?
> type : (one-of/c 'gif 'jpeg 'png 'xbm 'xpm 'bmp) = 'xpm

Saves the current content of viewport to file. The type argument determines the kind of file that is written.
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