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Bug 4072

Summary: SVG images : add a parameter to control scaling of images
Product: SDL_image Reporter: Sylvain <sylvain.becker>
Component: miscAssignee: Sam Lantinga <slouken>
Status: NEW --- QA Contact: Sam Lantinga <slouken>
Severity: normal    
Priority: P2 CC: danintheshed
Version: unspecified   
Hardware: All   
OS: All   

Description Sylvain 2018-02-08 09:28:21 UTC 
SDL_image handles SVG image. It currently loads them with their original width/heigh.

It would be nice to be able to use the rasterized scale parameter, so that those images could be loaded with any width/height. (it's not possible to modify the aspect ratio though). 


To have this done use in one pass (in IMG_LoadSVG_RW), we can think of 4 modes: 

none: current behaviour, scale is 1.0f. Output surface is (image->width) x (image->height).

user_scale: user provides scale parameter. Output surface is (image->width * user_scale) x (image->height * user_scale). The drawback with this, is that user doesn't know in advance the output width/height.

user_width: user provides output width. So scale is computed as (user_width / image->width). Output surface is (user_width) x (image->height * (user_width / image->width)).

user_height: user provides output height. So scale is computed as (user_height / image->height). Output surface is (image->width * (user_height / image->height)) x (user_height).


I think that the purpose of vector images to control the scale parameter !
Comment 1 Dan Lawrence 2020-05-15 18:17:08 UTC 
The current behaviour of SVG is a little odd, it seems to create the surface size based on the values defined in the svg files 'width' and 'height' parameters. e.g.

<?xml version="1.0"?>
<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 60 30" preserveAspectRatio="none" width="240" height="120">
<clipPath id="s">
	<path d="M0,0 v30 h60 v-30 z"/>
</clipPath>
<clipPath id="t">
	<path d="M30,15 h30 v15 z v15 h-30 z h-30 v-15 z v-15 h30 z"/>
</clipPath>
<g clip-path="url(#s)">
	<path d="M0,0 v30 h60 v-30 z" fill="#012169"/>
	<path d="M0,0 L60,30 M60,0 L0,30" stroke="#fff" stroke-width="6"/>
	<path d="M0,0 L60,30 M60,0 L0,30" clip-path="url(#t)" stroke="#C8102E" stroke-width="4"/>
	<path d="M30,0 v30 M0,15 h60" stroke="#fff" stroke-width="10"/>
	<path d="M30,0 v30 M0,15 h60" stroke="#C8102E" stroke-width="6"/>
</g>
</svg>

The SVG file will load onto a surface that is 240x120 pixels, but the image of the flag it contains will only be 60x30 pixels

I think a more useful default behaviour here would be to scale the flag's width to match the surface's width in the rasterize step. 

Unless I'm getting something wrong - I am loading at a remove via pygame.