Arnaldo Badin Arnaldo Badin - 1 year ago 145
C++ Question

Create texture from sprite_sheet coordinates

I have a sprite_sheet (example sheet):

This is an example, this is not my own authority.

I loaded as vector data and I need to make a new texture from a specified area. Like this:

glMakeTexture([0, 0], [50, 50], configs, etc) //to display only one sqm.

enter image description here

But i don't know how couse mostly GL functions only works in full area, like glTexImage2D.

Have a way to do that without load the full sprite_sheet as a texture?

OBS: I'm using picoPNG to decode PNG and I CAN load png, but not make a texture from specified area.

Answer Source

Because you show no code I assume that:

char *data; // data of 8-bit per sample RGBA image
int w, h; // size of the image
int sx, sy, sw, sh; // position and size of area you want to crop.

glTexImage2D does support regions-of-interest. You do it as follows:

glPixelStorei(GL_UNPACK_ROW_LENGTH, w);
glPixelStorei(GL_UNPACK_SKIP_PIXELS, sx);
glPixelStorei(GL_UNPACK_SKIP_ROWS, sy);
glPixelStorei(GL_UNPACK_ALIGNMENT, 1); // LodePNG tightly packs everything
glTexImage2D(GL_TEXTURE_2D, level, internalFormat, sw, sh, border, format, type, data);
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