Fix problem with textured triangle in cpp sdl2

Question

I make my own voxel engine and when I set texture on trinagle it looks weird and not correct here my triangle render code:

vertices[0].position.x = draw_face.point0.x;
vertices[0].position.y = draw_face.point0.y;
vertices[0].tex_coord = {float(draw_face.t_ind0.x), float(draw_face.t_ind0.y)};
vertices[0].color = {
    (unsigned char)(255 - (int)(draw_face.point_shadow0)), 
    (unsigned char)(255 - (int)(draw_face.point_shadow0)), 
    (unsigned char)(255 - (int)(draw_face.point_shadow0)), 
    255
};
            

vertices[1].position.x = draw_face.point1.x;
vertices[1].position.y = draw_face.point1.y;
vertices[1].tex_coord = {float(draw_face.t_ind1.x), float(draw_face.t_ind1.y)};
vertices[1].color = {
    (unsigned char)(255 - (int)(draw_face.point_shadow1)), 
    (unsigned char)(255 - (int)(draw_face.point_shadow1)), 
    (unsigned char)(255 - (int)(draw_face.point_shadow1)), 
    255
};


vertices[2].position.x = draw_face.point2.x;
vertices[2].position.y = draw_face.point2.y;
vertices[2].tex_coord = {float(draw_face.t_ind2.x), float(draw_face.t_ind2.y)};
vertices[2].color = {
    (unsigned char)(255 - (int)(draw_face.point_shadow2)), 
    (unsigned char)(255 - (int)(draw_face.point_shadow2)), 
    (unsigned char)(255 - (int)(draw_face.point_shadow2)), 
    255
};
SDL_RenderGeometry(renderer, texture, vertices, 3, NULL, 4);

when camera angle is 0:

enter image description here

and this is the my problem when camera is rotated:

enter image description here

HolyBlackCat · Accepted Answer · 2024-12-24 14:17:59Z

2

SDL interpolates the texture coordinates linearly, while you're asking for a perspective correct interpolation.

I don't think SDL_RenderGeometry() supports this. (Unless you're willing to draw each texel as a separate quad?)

Now might be a good time to learn the new rendering API shipped in SDL3, which should have no problems with this.

answered Dec 24, 2024 at 14:17

HolyBlackCat

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