Tutorial: Clipping in Gideros with renderTarget

keszegh · February 2014

I made this tutorial to summarize my findings about renderTarget and clipping, i hope you will find it useful:

http://www.indiedb.com/tutorials/clipping-in-gideros-with-rendertarget

john26 · February 2014

Very nice. But on my browser the screenshots are very blurred... Also I would recommend fewer blank lines and more indentation in the source code snippets.

keszegh · February 2014

you are right, about blurring, i could not repair it, i needed to upload the images here:
http://www.indiedb.com/members/longtitleproductions/images
and then embed them. yet however size i embed them the top part is blurred.

about code indentation and gaps, they just pasted in this ugly way when i copy-pasted. i plan to repair it once manually, but i was too tired at the end of copying and formatting all the text into the editor on indiedb. actually in an odt document i spent a lot of time to change the font for all the in-text words that refer to lua code words, but all of this was lost as well when copy-pasting, and after playing with it a bit, i gave up to find the appropriate way to copy.

keszegh · February 2014

so i corrected the code indentations and line gaps.
about blurred images, i played around a while, but i cannot make them better. it's how indiedb embeds them. if you know any solution, let me know.

altai · February 2014

@keszegh nice tutorial.
About blurred images, I think directly you should add your images links by "insert/add image" button through editor toolbox instead of embed code. Embed code automatically offers reduced size of your images.

keszegh · February 2014

you were right, the automatically offered embed code was for a small thumbnail, so copying directly the image link made it work. thanks for the comments and helps.

john26 · February 2014

Great! It looks much better now. Well done, I can see you have put in lots of work on this.

keszegh · February 2014

Finally my tutorial was added to the main tutorial page of indiedb, so this way more people will see it and get to know about Gideros as well:
http://www.indiedb.com/tutorials

hgvyas123 · April 2014

Nice tutorial. i wonder are there any other thing we can do with rendertarget???

keszegh · April 2014

@hgvyas123,
the possibilities are endless, eg. one natural use is a small map of the play area, done by simply rendering to a rendertarget and scaling down an image which has this rendertarget as a texture.

i also use it in a similar way to have a slider in my drawing app for stroke thickness, and then in another place in an always visible 'state' area i make a small copy of this slider. with rendertarget i can put several such items together to make a consise 'state' area showing several informations.
this way when e.g. the slider is not visible, because some other submenu is active, you still have a feedback in the 'state' area about the actual thickness of the stroke.

hgvyas123 · April 2014

Hmmm nice usage. Thanks for the info

keszegh · April 2014

i just wanted to let you know that this and my other tutorial on indiedb were each seen over 700 times (and so at least this many people are interested in gideros), which seems to be a nice number for me, although i never know if my own visits are counted multiple times or not.

john26 · April 2014

I've recently been working on a feature that badly needs clipping. Your tutorial shows how to do this with renderTarget but is this really a good alternative to a dedicated clipping function? or is it more like a workaround. Do you think Gideros ALSO needs clipping or is renderTarget a generalisation of clipping would you say?

ar2rsawseen · April 2014

@john26 ofcourse it needs better internal solution and this is a temporary workaround due to OpenGL version limitation.

There will be some limitations, but there will be a proper clipping implementation in OpenGL 2.0 support.

keszegh · April 2014

@john26, yes, as @ar2rsawseen says, clipping is so essential, that it should have a clean gideros implementation in the future (and apparently there will be). meanwhile, with the workaround from the tutorial you can do it with quite enough flexibility, you just have to be a little careful about not adding the clipped sprite itself to the stage, rather add it to the appropriate sprite that is always redrawn to the rendertarget. besides these technicalities i expect that the to-be implementation of clipping in gideros 2 will be similar in usage as the class in my tutorial.

more important is that something that you cannot do now is masking, i.e. clipping a sprite with the transparency info of another. i hope this will be a feature in later gideros, as now it's almost impossible to make a decent workaround for this.

john26 · April 2014

I'm curious why glStencil was not used? This has been around since the first OpenGL AFAIK.

ar2rsawseen · April 2014

@john26 because stencil buffers does not seem to work on all devices:
https://bugreports.qt-project.org/browse/QTBUG-30528
http://stackoverflow.com/questions/21616147/opengl-es-stencil-buffer-not-working-on-specific-devices

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