Check-in [e9c252cf1d]

do not scale and are to tiny on high res mobile devices.
The same goes for the image formats provided by the img extension.

There is already an tk image extension at https://github.com/auriocus/tksvg
The implementation is using nanosvg. It has no other external dependencies
and is only 2 header files.

**nanosvg** was choosen because it:

- has a suitable license
- is written in 2 plain C header files and can easily included
- is really lightweight
- is tested with tksvg
- can render images
- has no other external dependencies

The original nanosvg project is hosted at https://github.com/memononen/nanosvg

# Specification

The already existing tksvg extension will be adapted and included in Tk.
A new image format will be created. The name is **svgnano**.
The choosen name hints the usage of a not fully compatible svg parser.
It leaves the image name **svg** open for further usage.

The **svgnano** image format has the following format suboptions:

**svgnano** *-dpi dpiValue -scale scaleValue -unit unitValue -x xValue -y yValue*

*dpiValue* is used in conversion between given coordiantes and screen resolution. The value must be greater then 0.0. The default value is 96.

*scaleValue* is used to scale the resulting image. The value must be greater then 0.0. The default value is 1.

*unitValue* is the unit of all coordinates in the svg data. Available units are px (default, coordinates in pixel), mm , cm and in.

*xValue* is used to move the created image in x-direction. The default value is 0.

*yValue* is used to move the created image in y-direction. The default value is 0.
.
The given format options are only used at creation time of the image and are not preserved in the image.

# Supported SVG

The svgnano format supports a wide range of SVG features, but something may be missing p.e. text.

## Elements

- g
- path
- rect
- circle
- ellipse
- line
- polyline
- polygon
- linearGradient
- radialGradient
- stop
- defs
- svg
- style

## Attributes

- width, height
- viewBox
- preserveAspectRatio with none, xMin, xMid, xMax, yMin, yMid, yMax, slice

## Gradient Attributes

- gradientUnits with objectBoundingBox
- gradientTransform
- cx, cy, r
- fx, fy
- x1, y1, x2, y2
- spreadMethod with pad, reflect or repeat
- xlink:href

## Poly Attributes

- points

## Line Attributes

- x1, y1, x2, xy2

## Ellipse Attributes

- cx, cy
- rx, ry

## Circle Attributes

- cx, cy
- r

## Rectangle Attributes

- x, y
- width, height
- rx, ry

## Path Attributes

- d with m, M, l, L, h, H, v, V, c, C, s, S, q, Q, t, T, a, A, z, Z

## Style Attributes

- display with none, visibility, hidden, visible
- fill with nonzero, evenodd
- opacity
- fill-opacity
- stroke
- stroke-width
- stroke-dasharray
- stroke-dashoffset
- stroke-opacity
- stroke-linecap with butt, round, square
- stroke-linejoin with miter round bevel
- stroke-miterlimit
- fill-rule
- font-size
- transform with matrix, translate, scale, rotate, skewX, skewY
- stop-color
- stop-opacity
- offset
- id
- class

# Discussion

- http://code.activestate.com/lists/tcl-core/19871/
- http://code.activestate.com/lists/tcl-core/19994/

## Open questions



- are all of the above format options necessary? May be remove the *xValue* abd *yValue* options.

# Implementation

A patch implementing these changes is available in the fossil repository in the [tip-507 branch]
(https://core.tcl.tk/tk/timeline?r=tip-507).

The new format is in the photo.n man page described.

# Example of use

	    # the image data