Check-in [7c6da1bc85]

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# Abstract

Image photo SVG support was added to Tk by TIP 507.
This TIP is about the options of SVG rendering:

   *   The option "-unit" is not helpful in an environment, where the only destination unit is pixel.
   *   The option "-scale float" is the essential tool to set rendering scaling. Nevertheless, to scale to a given height or width, a two-step procedure is required. This common case should be implemented by a one step procedure.
   *   A valid image file scaled to a size below 0.5px or 0.5px does not lead to an error but to an image of 1x1 pixels. The aspect-ratio is not respected.

# Rationale

This TIP included two components:

## Remove option "-unit"

Remove the option "-unit".
The given unit is used to set the unit of the intermediate set of polygons.

The final unit will be pixels anyway, undependent on any intermediate unit.
................................................................................
    p configure [list svg -scale [expr {double($height) / $imageHeight}]

This two step procedure has a high performance impact, as the image is loaded twice.
The aim is to render it only once by one parameter.

## No error on to small scale

It feels odd to throw an error on a valid image but on a to small -scale parameter resulting in a rounded size of width 0 or height 0.
Alternatively, a valid image with size 1x1 is rendered.

As an alternate solution, an error message special for this case may be given.

# Specification

## Remove option "-unit"

................................................................................
    8

The entier argument must be greater than 0.
The option may not be specified together with "-scale" and/or "-scaletoheight".

## No error on to small scale

The image size is set to 1x1 if wether width or height is 0 after scaling and rounding.
This is a very rare case, as ceil rounding is used and we must go below the resolution of double to acheve this.

# Implementation

Implementation is ready in branch tip-545-svg-options.
















# Copyright

This document has been placed in the public domain.

# Abstract

Image photo SVG support was added to Tk by TIP 507.
This TIP is about the options of SVG rendering:

   *   The option "-unit" is not helpful in an environment, where the only destination unit is pixel.
   *   The option "-scale float" is the essential tool to set rendering scaling. Nevertheless, to scale to a given height or width, a two-step procedure is required. This common case should be implemented by a one step procedure.
   *   A valid image file scaled to a size resulting to 0 px height or width does not lead to an error but to an image of at least 1x1 pixels. The aspect-ratio may not be respected.

# Rationale

This TIP includes the following proposed changes:

## Remove option "-unit"

Remove the option "-unit".
The given unit is used to set the unit of the intermediate set of polygons.

The final unit will be pixels anyway, undependent on any intermediate unit.
................................................................................
    p configure [list svg -scale [expr {double($height) / $imageHeight}]

This two step procedure has a high performance impact, as the image is loaded twice.
The aim is to render it only once by one parameter.

## No error on to small scale

It feels odd to throw an error on a valid image but on a to small combination of size and -scale parameter resulting in a rounded size of width 0 or height 0.
Alternatively, a valid image with width 1 and/or height 1 is rendered.

As an alternate solution, an error message special for this case may be given.

# Specification

## Remove option "-unit"

................................................................................
    8

The entier argument must be greater than 0.
The option may not be specified together with "-scale" and/or "-scaletoheight".

## No error on to small scale

The image size is set to height 1 and/or width 1 if width and/or height is 0 after scaling and rounding.
This is a very rare case, as ceil rounding is used and we must go below the resolution of double to acheve this.

# Implementation

Implementation is ready in branch tip-545-svg-options.

# Discussion

This TIP was discussed at Euro-TCL 2019.

It was concluded that svg support is a good feature and helpful for modern gui design.
The limitations of nanosvg are seen as ok.

It was concluded that there is no use case for the -unit option.

Rene has another use-case for visual graph generation.
A svg file is created on the fly using the given data.
This is then rendered and displayed by a label widget.
This procedure is faster than the canvas or the tkpath widget (and has much less features).
This solution is a good fit to this application.

# Copyright

This document has been placed in the public domain.