Canvas draw library

Tip  The basic canvas.draw library was merged into FGDATA in 03/2020 so it available by default now.

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Introduction

There are basically two ways to populate a canvas, loading an SVG file which has been created with some tool like inkscape, or by writing a nasal program that calls drawing functions of the canvas API.

Both ways are valid and have their pros and cons.

The canvas API was quite limited, only a few basic commands were available, so canvas.draw library was created to provide more drawing commands.

Note  Development of this library started in 12/2018 as a separate CanvasDrawDev add-on and is largely based on GPL'ed plot2D code written originally by Rodolfo (rleibner on the forums) as part of the Spoken GCA, PAR instrument and Oscilloscope add-ons.

Goals

• Make the code flexible and powerful so people will like to use it
• Provide complex drawing commands needed for e.g. compass rose or speed tapes
• Provide easy to use styles

canvas.draw API

draw module

Note  All draw methods expect a canvas group element 'cgroup' as first parameter to draw on.

draw.colors

A hash with some standard colors like white, black, red, green, blue, cyan, magenta, yellow, orange. Just in case you need them ;)

circle()

circle(cgroup, radius, center_x = nil, center_y = nil)

radius in pixel

center_x, center_y optional center of circle

ellipse()

ellipse(cgroup, radius, center_x = nil, center_y = nil)

radius_x, radius_y in pixel

center_x, center_y optional center of ellipse

arc()

circular marks

arc(cgroup, radius, center, from_deg = nil, to_deg = nil)

Draw an arc (part of a circle) with given radius around center. In the example image a red, green and blue arc are shown, nasal code below.

center center point of circle as vector [x,y]

from_deg, to_deg start and end of arc in degree of compass rose (0 = North, 90 = East, ...); defaults to 0, 360 (full circle)

    # [CX, CY] center point
    var start = -40;
    canvas.draw.arc(myGroup, radius, [CX, CY], start, start+190).setColor(COLORS["red"]);
    start += 90;
    canvas.draw.arc(myGroup, radius, [CX, CY], start, start+270).setColor(COLORS["green"]);
    start += 90;
    canvas.draw.arc(myGroup, radius, [CX, CY], start, start+190).setColor(COLORS["blue"]);

rectangle()

rectangle(cgroup, width, height, x = 0, y = 0, rounded = nil)

width, height dimensions in pixels

x, y top-left corner of rectangle

rounded optional radius of corners in pixel

square()

square(cgroup, length, center_x = 0, center_y = 0, cfg = nil)

shorthand for rectangle with width = height = length

deltoid()

deltoid (cgroup, dx, dy1, dy2, x = 0, y = 0)

Deltoid draws a kite (dy1 > 0 and dy2 > 0) or a arrow head (dy2 < 0).

dx width

dy1 height of "upper" triangle

dy2 height of "lower" triangle, < 0 draws an arrow head

x, y position of tip

    var dx = 40;
    #rhombus draws around a center point while deltoid uses x,y for tip point
    shapes["rhombus1"] = canvas.draw.rhombus(group, dx, 2*dx, 5 + dx/2, CY)
        .setColor(COLORS["cyan"]);

    # width = 40, height = 25 + 50;
    shapes["deltoid1"] = canvas.draw.deltoid(group, dx, 25, 50, 2*dx, CY)
        .setColor(COLORS["magenta"]);

    # y2 < 0 results in arrow head
    canvas.draw.deltoid(group, dx, 2*dx, -dx, 4*dx, CY)
        .setColor(COLORS["yellow"]);

    # y2 = 0 results in triangle
    canvas.draw.deltoid(group, dx, 2*dx, 0, 6*dx, CY)
        .setColor(COLORS["green"]);

    # y2 < 0 and |y2| > y1 results in arrowhead with tip above baseline
    canvas.draw.deltoid(group, dx, 1.5*dx, -2.5*dx, 8*dx, CY)
        .setColor(COLORS["red"]);

rhombus() / diamond()

rhombus: func(cgroup, dx, dy, center_x = 0, center_y = 0)

draws a diamond around [center_x, center_y] (first element from left in sample image above)

dx width

dy height

grid()

Draw horizontal and verical lines. Two signatures are available

1) (cgroup, [sizeX, sizeY], dx, dy, border = 1)

2) (cgroup, nx, ny, dx, dy, border = 1)

size [width, height] of grid in pixels.

nx, ny number of lines in x/y direction

dx, dy distance between lines in pixels.

border optional boolean, draw lines at sizeX and sizeY, true by default.

    var group = myRoot.createChild("group", "grid_scales");
    #-- grid test --
    canvas.draw.grid(group, [62, 55], 10, 10, 0).setTranslation(10, 100);
    canvas.draw.grid(group, [62, 55], 10, 10, 1).setTranslation(100, 100);
    canvas.draw.grid(group, 4, 4, 20, 10, 0).setTranslation(10, 200);
    canvas.draw.grid(group, 4, 4, 20, 10, 1).setTranslation(100, 200);

Marks

Marks can be used to create scales / gauges.

marksLinear()

linear marks (horizontal)

linear marks (vertical)

marksLinear(cgroup, orientation, num_marks, interval, style)

Draw marks for a linear scale on a canvas group, e.g. speed tape. Mark lines are draws perpendicular to baseline.

orientation of baseline, "up", "down" (="vertical"), "left", "right" (="horizontal"), only first character is evaluated (u,d,v,l,r,h).

num_marks number of marks to draw

interval distance between marks (pixel)

style marksStyle hash with more parameters

    #-- marks for linear scales --
    var group = myRoot.createChild("group", "marks");
    var style = canvas.draw.marksStyle.new()
        .setBaseline(1)
        .setMarkLength(0.8)     # 0.8 * interval
        .setSubdivisions(2);
    
    canvas.draw.marksLinear(group, "right", 5, 30, style).setTranslation(CX, 150)
        .setColor(COLORS["green"]);
    
    style.setSubdivisions(1);
    style.setMarkOffset(style.MARK_LEFT); # left/up
    canvas.draw.marksLinear(group, "v", 5, 20, style).setTranslation(50, CY)
        .setColor(COLORS["red"]);
    canvas.draw.marksLinear(group, "h", 4, 20, style).setTranslation(CX, 30)
        .setColor(COLORS["red"]);
    style.setMarkOffset(style.MARK_CENTER); #center
    canvas.draw.marksLinear(group, "down", 5, 20, style).setTranslation(100, CY)
        .setColor(COLORS["green"]);
    canvas.draw.marksLinear(group, "left", 4, 20, style).setTranslation(CX, 70)
        .setColor(COLORS["green"]);
    style.setMarkOffset(style.MARK_RIGHT); #right / down
    canvas.draw.marksLinear(group, "up", 5, 20, style).setTranslation(150, CY)
        .setColor(COLORS["blue"]);
    canvas.draw.marksLinear(group, "r", 4, 20, style).setTranslation(CX, 110)
        .setColor(COLORS["blue"]);

marksCircular()

circular marks

marksCircular(cgroup, radius, interval, phi_start = 0, phi_stop = 360, style = nil)

draw marks along an arc or circle of given radius

radius of baseline (circle)

interval distance of marks in degree

phi_start position of first mark in degree (default 0 = north)

phi_stop position of last mark in degree (default 360)

    #-- marks on arc / circle --
    style.setMarkLength(0.1);
    style.setMarkOffset(style.MARK_IN); # pointing to center
    style.setSubdivisions(2);
    style.setBaseline(1);
    var radius = 150;
    var interval = 30;
    canvas.draw.marksCircular(group, radius, interval, 30, 120, style)
        .setTranslation(CX,CY);

    style.setMarkOffset(style.MARK_OUT); # pointing outside
    style.setSubdivisions(1);
    radius = 90;
    interval = 10;
    canvas.draw.marksCircular(group, radius, interval, 0, 360, style)
        .setTranslation(CX,CY)
        .setColor(COLORS["cyan"]);

draw.style

Base class for styles.

draw.marksStyle

Parameter hash for drawing marks (see above).

new()

Create a new style instance.

var myMarkStyle = canvas.draw.marksStyle.new()

setMarkLength()

Set length of marker in %interval or %radius

setMarkOffset()

Set alignment of markers.

You can use marksStyle.MARK_LEFT marks left of vertical baseline

MARK_UP marks above horizontal baseline

MARK_CENTER marks centered on baseline

MARK_RIGHT marks right of vertical baseline

MARK_DOWN marks below horizontal baseline

var myMarkStyle = canvas.draw.marksStyle.new()
myMarkStyle.setMarkOffset(myMarkStyle.MARK_LEFT);

setMarkWidth()

Set line width in pixel.

setSubdivisions()

Set number of subdivisions (default = 0).

setSubdivisionLength()

Set length of subdivision marker in %marker_length

transform module

The following methods are available to manipulate existing canvas elements.

Note  This chapter is a draft, see FGDATA/Nasal/canvas/draw/transform.nas for details

Note  All transform methods expect a canvas element as first parameter.

move()

params: elem, dx, dy

rotate()

params: elem, deg, center

flipX()

params: elem, xaxis = 0

mirror element on x-axis

flipY()

params: elem, yaxis = 0

mirror element on y-axis

alignX()

Aligns the element, moving it horizontaly to ref.

params:

elem element to be moved.

ref reference may be an integer or another element.

alignment as string: may be 'left-left', 'left-center', 'left-right', 'center-left', 'center-center', 'center-right', 'right-left', 'right-center', 'right-right'. If ref is a single number, the 2nd word is ignored.

alignY()

Aligns the element, moving it vertically to ref.

params:

elem element to be moved.

ref reference may be an integer or another element.

alignment as string: may be 'top-top', 'top-center', 'top-bottom', 'center-top', 'center-center', 'center-bottom', 'bottom-top', 'bottom-center', 'bottom-bottom'. text elements also accept 'baseline' as reference. If ref is a single number, the 2nd word is ignored.

rotate180()

params: elem, center = nil

center as [x,y] in pixels, otherwise: rotate in place

scaleX()

Stretch element horizontally

params:

elem element to be stretched.

factor the new-width/old-width ratio.

ref the relative point to keep inplace. May be 'left', 'center' or 'right'.

scaleY()

strech element vertically

params:

elem element to be stretched.

factor the new-height/old-height ratio.

ref the relative point to keep inplace. May be 'top', 'center' or 'bottom'.

resize()

params:

elem element to be stretched.

factors as vector [Xfactor, Yfactor]

ref the relative point to keep inplace:

may be 'left-top', 'left-center', 'left-bottom', 'center-top', 'center-center', 'center-bottom', 'right-top', 'right-center', 'right-bottom'.

References

CompassRose is based on canvas draw.

Note  You can test, improve and play around with canvas.draw by downloading the CanvasDrawDev add-on.