How do I read the RGBA values of a pixel from a surface or texture
with SDL2?
lazarus / 39-Graphics

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semichaud1 · 2019-12-01 16:26

Hi,

How do I read the RGBA values of a specific pixel, at given
coordinates x and y, from a surface or texture with SDL2 in Free
Pascal?

Thanks.

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piXelicidio · 2019-12-17 13:45

Hi, you can't or shouldn't read pixels from a texture because its on
GPU memory.
Only from surfaces:
When you create the surface with
(https://wiki.libsdl.org/SDL_CreateRGBSurface) maybe with 32 bits in
the deph parameter.
Then it returns an structure (record):
https://wiki.libsdl.org/SDL_Surface
There you can get and access anytime the "pixels" pointer.
From that record you need also pitch to make your custom getpixel and
setpixel.

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metis · 2019-12-20 17:09

@semichaud1

and then try it with
SDL_GetDisplayDPI(...);  // Get diagonal, horizontal, vertical DPI
and
SDL_GetRGBA(...); // Get the Pixel's RGBA-Values

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metis · 2020-05-30 14:49

@semichaud1

with 'SDL_RenderReadPixels()' you may get the Pixels from a Texture
w/o creating a Surface in Your Code, see:
https://discourse.libsdl.org/t/most-efficient-way-of-getting-render-
pixels/27581.