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Create new white texture from existing SDL_Texture.

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7 replies to this topic

#1 Sunsharior   Members   


Posted 05 April 2014 - 04:28 PM

Hello everyone,


I'm trying to accomplish something in SDL and i'm wondering if it can be done easily.


What i want to do it this:


First i create a new texture from a PNG file with this code. No problem so far.

bool CTextureInfo::Unserialize(std::ifstream &_inputfilestream)
    int pngsize = 0;
    _inputfilestream.read(reinterpret_cast<char *>(&pngsize), sizeof(int) );
    char *textureBinaries = new char[pngsize];
    _inputfilestream.read(reinterpret_cast<char *>(textureBinaries), pngsize);
    // Create texture
    SDL_RWops *img = SDL_RWFromConstMem(textureBinaries, pngsize);
    // This part is building the texture through SDL_image
    SDL_Texture *texture = IMG_LoadTexture_RW(CSDL_Setup::GetInstance()->GetRenderer(), img, 0);

After this i want to create another texture that will be a copy of the first one, but instead all pixels that are not transparent become white.

See attached image for example of what texture 1 and texture 2 should look like.


However, i am failing really hard to figure how to do this.

I thank you in advance.



Attached Thumbnails

  • bladewhite.png

#2 dejaime   Members   


Posted 05 April 2014 - 08:08 PM

The most direct approach would be to use color modulation (SDL_SetTextureColorMod) to something really high (like 255) and then using a RenderCopy to the new texture. It would work if none of your rgb values are 0. 


But, given this limitation, you have a second option. You go and read the first texture pixel per pixel and, if it is not magic-pink, render a white pixel on the other texture with the same coordinates. You could also compute the "biggest non-invisible rectangle" and draw it, reducing significantly the drawing calls.


It is important to tell, Textures are really awesome for rendering, super fast and all. But you'll have a hard time trying to edit them. This type of editions in SDL2 is usually done using surfaces.


PS: Assuming you're using SDL2 (what you should, SDL1 is LGPL).

Edited by dejaime, 05 April 2014 - 08:09 PM.

#3 Sunsharior   Members   


Posted 05 April 2014 - 08:30 PM

Color modulation is the first thing i tried to do, but i noticed setting it to 255, 255, 255 don't change the color.

I attached an image of what i tried to do earlier today.


First image is a colorModulation with the normal weapon.

Second image is a colorModulation with a white image (White shadow) of the weapon.


IMO it look so much better in the second image. Note that i would actually change the white blade for the actual blade if i manage to find something that work smile.png


Right now, i'm trying to do the second thing you said, dejaime. I'm trying to convert the texture to a surface and change all pixel to white.

Oh boy, google is really not helping me on this one, maybe i'm trying to do something very easy in a very complicated way, ahah.


Edit: Yes, i'm using SDL2. I also know texture are way faster than surface, this is why i'm trying to avoid using surfaces altogether.

Attached Thumbnails

  • bladetrail.png

Edited by Sunsharior, 05 April 2014 - 08:36 PM.

#4 dejaime   Members   


Posted 06 April 2014 - 07:12 AM

Here, take a look:
The interesting part is the line 73. The function that actually does the job is defined at the end of the file.
Pardon the lack of cleanup, I'm just too lazy!

Got that image from here.

Edited by dejaime, 06 April 2014 - 07:33 AM.

#5 Sunsharior   Members   


Posted 06 April 2014 - 07:33 AM

Dejaime! Thank you so much! This has solved my problem exactly how i described it. If i could vote you up one thousand time, i would!


Attached Thumbnails

  • weapontrailsucess.png

#6 dejaime   Members   


Posted 06 April 2014 - 08:34 AM

We're all here to help and learn!

#7 Lactose   GDNet+   


Posted 06 April 2014 - 12:25 PM

Another way would be to do this pre-process -- actually creating both versions of the image and loading both files.


It shouldn't be too difficult to do this with e.g. Photoshop and using a batch/macro. This could also allow you to add various effects (e.g. blur or something) to the image, and potentially manually adjust specific images if needed.


That said, this would also mean more files and larger disk footprint, which is something to keep in mind.

Hello to all my stalkers.

#8 Sunsharior   Members   


Posted 16 April 2014 - 08:12 PM

I'm taking the liberty to update this topic in case anyone else is trying to do the same thing i did earlier this month.


I have found that dejaime's solution work perfectly fine for 32-bits images, but i got error as soon as i switched to 24-bits.


To solve this, refer to this documentation http://sdl.beuc.net/sdl.wiki/Pixel_Access


Have a good day!

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