Draw dialect

Abstract

Draw is a dialect (DSL) of Red language that provides a simple declarative way to specify 2D drawing operations. Such operations are expressed as lists of ordered commands (using blocks of values), which can be freely constructed and changed at run-time.

Draw blocks can be rendered directly on top of an image using the draw function, or inside a View face using the draw facet (see View documentation).

Commands

Commands can be drawing instructions or settings for the drawing instructions. When a mode is set, it will affect all subsequent operations in the current Draw session (or until changed).

Most drawing commands require coordinates to be specified. The 2D coordinate system used is:

  • x axis: increasing from left to right of the display.
  • y axis: increasing from up to bottom of the display.

Some drawing commands require lengths to be specified. The length required is number of pixels.

List of Draw commands:

Line

Syntax

line <point> <point> ...

<point> : coordinates of a point (pair!).

Description

Draws a line between two points. If more points are specified, additional lines are drawn, connecting each point in the provided order.

Triangle

Syntax

triangle <point> <point> <point>

<point> : coordinates of a vertex of the triangle (pair!).

(Note: A vertex is the point at which two lines meet. They are points where edges join.)

Description

Draws a triangle with edges between the supplied vertices.

Box

Syntax

box <top-left> <bottom-right>
box <top-left> <bottom-right> <corner>

<top-left>     : coordinates of the top-left of the box (pair!).
<bottom-right> : coordinates of the bottom-right of the box (pair!).
<corner>       : (optional) radius of the arc used to draw a round corner (integer!).

Description

Draws a box using the top-left (first argument) and bottom-right (second argument) vertices. An optional radius can be provided for making round corners.

Polygon

Syntax

polygon <point> <point> ...

<point> : coordinates of a vertex (pair!).

Description

Draws a polygon using the provided vertices. The last point does not need to be the starting point, an extra line will be drawn anyway to close the polygon. Minimal number of points to be provided is 3.

Circle

Syntax

circle <center> <radius>
circle <center> <radius-x> <radius-y>

<center>   : coordinates of the circle's center (pair!).
<radius>   : radius of the circle (integer!).
<radius-x> : (ellipse mode) radius of the circle along X axis (integer!).
<radius-y> : (ellipse mode) radius of the circle along Y axis (integer!).

Description

Draws a circle from the provided center and radius values. The circle can be distorted to form an ellipse by adding an optional integer indicating the radius along Y axis (the other radius argument then becomes the radius along X).

Ellipse

Syntax

ellipse <top-left> <size>

<top-left> : coordinates of the ellipse's bounding box top-left point (pair!).
<size>     : size of the bounding box (pair!).

Description

Draws an ellipse from the specified bounding box. The size argument represents the X and Y diameters of the ellipse.

Note: ellipse provide a more compact and box-oriented way to specify a circle/ellipse compared to circle command.

Arc

Syntax

arc <center> <radius> <begin> <end>
arc <center> <radius> <begin> <end> closed

<center> : coordinates of the circle's center (pair!).
<radius> : radius of the circle (pair!).
<begin>  : starting angle in degrees (integer!).
<end>  : ending angle in degrees (integer!).

Description

Draws the arc of a circle from the provided center and radius values. The arc is defined by two angles values. An optional closed keyword can be used to draw a closed arc using two lines coming from the center point.

Curve

Syntax

curve <end-A> <control-A> <end-B>
curve <end-A> <control-A> <control-B> <end-B>

<end-A>     : end point A (pair!).
<control-A> : control point A (pair!).
<control-B> : control point B (pair!).
<end-B>     : end point B (pair!).

Description

Draws a Bezier curve from 3 or 4 points:

  • 3 points: 2 end points, 1 control point.
  • 4 points: 2 end points, 2 control points.

Four points allow more complex curves to be created.

Spline

Syntax

spline <point> <point> ...
spline <point> <point> ... closed

<point> : a control point (pair!).

Description

Draws a B-Spline curve from a sequence of points. At least 3 points are required to produce a spline. The optional closed keyword will draw an extra segment from the end point to the start point, in order to close the spline.

Note: 2 points are accepted, but they will produce only a straight line.

Image

Syntax

image <image>
image <image> <top-left>
image <image> <top-left> <bottom-right>
image <image> <top-left> <top-right> <bottom-left> <bottom-right>
image <image> <top-left> <top-right> <bottom-left> <bottom-right> <color>
image <image> <top-left> <top-right> <bottom-left> <bottom-right> <color> border

<image>        : image to display (image! word!).
<top-left>     : (optional) coordinate of top left edge of the image (pair!).
<top-right>    : (optional) coordinate of top right edge of the image (pair!).
<bottom-left>  : (optional) coordinate of bottom left edge of the image (pair!).
<bottom-right> : (optional) coordinate of bottom right edge of the image (pair!).
<color>        : (optional) key color to be made transparent (tuple! word!).

Description

Paints an image using the provided information for position and width. If the image has positioning information provided, then the image is painted at 0x0 coordinates. A color value can be optionally provided, it will be used for transparency.

Note:

  • Four points mode is not yet implemented. It will allow to stretch the image using 4 arbitrary-positioned edges.
  • border optional mode is not yet implemented.

Text

Syntax

text <position> <string>

<position> : coordinates where the string is printed (pair!).
<string>   : text to print (string!).

Description

Prints a text string at the provided coordinates using the current font.

Note: If no font is selected or if the font color is set to none, then the pen color is used instead.

Font

Syntax

font <font>

<font> : new font object to use (object! word!).

Description

Selects the font to be used for text printing. The font object is a clone of font!.

Pen

Syntax

pen <color>

<color> : new color to use for drawing (tuple! word!).

Description

Selects the color to be used for line drawing operations.

Fill-pen

Syntax

fill-pen <color>
fill-pen off

<color> : new color to use for filling (tuple! word!).

Description

Selects the color to be used for filling operations. All closed shapes will get filled by the selected color until the fill pen is set to off.

Line-width

Syntax

line-width <value>

<value> : new line width in pixels (integer!).

Description

Sets the new width for line operations.

Line-join

Syntax

line-join <mode>

<mode> : new line joining mode (word!).

Description

Sets the new line joining mode for line operations. Following values are accepted:

  • miter (default)
  • round
  • bevel
  • miter-bevel

Note: miter-bevel mode selects automatically one or the other joining mode depending on the miter length (See this.aspx) for detailed explanation).

Line-cap

Syntax

line-cap <mode>

<mode> : new line cap mode (word!).

Description

Sets the new line's ending cap mode for line operations. Following values are accepted:

  • flat (default)
  • square
  • round

Anti-alias

Syntax

anti-alias <mode>

<mode> : `on` to enable it or `off` to disable it.

Description

Turns on/off the anti-aliasing mode for following Draw commands.

Note: Anti-aliasing gives nicer visual rendering, but degrades performances.

Default values

When a new Draw session starts, the following default values are used:

Property Value
background white
pen color black
filling off
anti-alias on
font none
line width 1
line join miter
line cap flat

Sub blocks

Inside Draw code, commands can be arbitrarily grouped using blocks. Semantics remain unchanged, this is currently just a syntactic sugar allowing easier group manipulations of commands (notably group extraction/insertion/removal). Empty blocks are accepted.

Source position

Set-words can be used in the Draw code in-between commands to record the current position in Draw block and be able to easily access it later.

Note: if the Draw block length preceeding a set-word is changed, the recorded position is not updated.

Draw function

It is possible to render a Draw block directly to an image using the draw function.

Syntax

draw <size> <spec>
draw <image> <spec>

<size>  : size of a new image (pair!).
<image> : image to use as canvas (image!).
<spec>  : block of Draw commands (block!).

Description

Renders the provided Draw commands to an existing or a new image. The image value is returned by the function.

Graphics source code

The graphics in this documentation are generated using Red and Draw dialect, here is the source code (you can copy/paste it in a Red console to try/play/improve it):

Red [
    Title:    "Graphics generator for Draw documentation"
    Author: "Nenad Rakocevic"
    File:   %draw-graphics.red
    Needs:    View
]

Arial: make font! [name: "Consolas" style: 'bold]
small: make font! [size: 9 name: "Consolas" style: 'bold]

save %line-cap.png draw 240x240 [
    font Arial
    text 20x220  "Flat"
    text 90x220  "Square"
    text 180x220 "Round"

    line-width 20 pen gray
    line-cap flat    line 40x40  40x200
    line-cap square line 120x40 120x200
    line-cap round    line 200x40 200x200

    line-width 1 pen black
    line 20x40  220x40
    line 20x200 220x200
]

save %line-join.png draw 500x100 [
    font Arial
    text 10x20  "Miter"
    text 170x20 "Round"
    text 330x20 "Bevel"

    line-width 20 pen gray
    line-join miter line 140x20 40x80  140x80
    line-join round line 300x20 200x80 300x80
    line-join bevel line 460x20 360x80 460x80

    line-join miter
    line-width 1 pen black
    line 140x20 40x80  140x80
    line 300x20 200x80 300x80
    line 460x20 360x80 460x80
]

save %coord-system.png draw 240x240 [
    font small
    text 5x5 "0x0"
    line-width 2
    line 20x20 200x20 195x16
    line 200x20 195x24

    line 20x20 20x200 16x195
    line 20x200 24x195

    font Arial
    text 205x12 "X"
    text 12x205 "Y"
]