Re: trying to do a blinking text cursor

To invert existing colors on a render target, you have to read the pixels
first so you can calculate the inverted colors.  This is a very slow
operation and should not be done lightly.

The best way to do it nowadays (i.e. without direct video memory access) is
to use a shader and keep the color calculations on the GPU.  I can't help
any further than that with plain SDL (is anyone using shaders with
SDL_Renderer?), but I can do it all in a couple minutes with SDL_gpu.

Jonny D



On Sat, Aug 6, 2016 at 11:20 AM, Jack Andrews <[email protected]> wrote:

> Hi,
>
> I'm using SDL2 as it looks like the most cross-platform UI library out
> there.  I don't want a GUI toolkit.
>
> I'm writing a very simple text editor and so far, the most challenging
> thing has been showing a blinking cursor at the text insertion point.
>
> I think I can work how an SDL timer works, but I can't work out how to
> invert the colours of a SDL_Rect at the insertion point.  How would I
> implement a function:
>
>   int ColourInvert(SDL_Window*w, SDL_Renderer*rend, SDL_Rect area);
>
> ?
>
> here's my pseudo-code for my editor (had to trim all the editor stuff out):
>
> SDL_Renderer*re;SDL_Window*w;TTF_Font*font;
> int drawline(char*s){
>   SDL_Surface*su=SDL_RenderText_Shaded(font,s,a,b));
>   SDL_Texture*tx=SDL_CreateTextureFromSurface,(re,su));
>   SDL_RenderCopy(re,tx,0,&rect));
>   SDL_DestroyTexture(tx);
>   SDL_FreeSurface(su);
> }
> main(){
>   SDL_Init(SDL_INIT_EVERYTHING);TTF_Init();
>   w=SDL_CreateWindow(x,a,a,y,z,SDL_WINDOW_SHOWN);
>   re=SDL_CreateRenderer(w,-1,SDL_RENDERER_ACCELERATED);
>   SDL_SetRenderDrawColor(g.v,255,255,255,255);
>   SDL_RenderClear(g.v);
>   SDL_RenderPresent(g.v);
>   //message loop
>   //a keypress changes a line
>   // for each line in lines{drawline(line)}
> }
>
> Thanks for all your work, guys,
>
>
> Jack
>
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>

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