c++ - Missing faces when displaying STL data -


i wrote simple parser ascii stl format. when try render triangles supplied normals, resulting object missing many faces:

this how should like:

what tried:

  • explicitly disabled backface culling (though shouldn't have been active before)
  • ensured depth buffer enabled

here minimal sample program reproduces error:

 #include <sdl2/sdl.h>  #include <sdl2/sdl_main.h>  #include <sdl2/sdl_render.h>  #include <sdl2/sdl_opengl.h>  int main(int argc, char **argv) {     sdl_init(sdl_init_video);     int screen_w=1280,screen_h=720;     sdl_window * win = sdl_createwindow("test", 20, 20, screen_w, screen_h,             sdl_window_opengl);     sdl_glcontext glcontext = sdl_gl_createcontext(win);       stlparser stlparser;     std::ifstream file(".\\logo.stl");     stlparser.parseascii(file);     const auto& ndata = stlparser.getndata();     const auto& vdata = stlparser.getvdata();     std::cout << "number of facets: " << ndata.size() << std::endl;      sdl_gl_setattribute(sdl_gl_doublebuffer, 1);       glmatrixmode(gl_projection | gl_modelview);     glloadidentity();     glscalef(1.f, -1.f, 1.f);     glortho(0, screen_w, 0, screen_h, -screen_w, screen_w);      glcleardepth(1.0f);     gldepthfunc(gl_lequal);     glenable(gl_depth_test);      gldisable(gl_cull_face);      glenableclientstate(gl_normal_array);     glenableclientstate(gl_vertex_array);      glnormalpointer(gl_float, 0, ndata.data());     glvertexpointer(3, gl_float, 0, vdata.data());      sdl_event event;     bool quit = false;      while (!quit) {         while (sdl_pollevent(&event))             switch(event.type) {             case sdl_quit: quit = true; break;             }             ;         // drawing         glclearcolor(255,255,255,255);         glclear(gl_color_buffer_bit | gl_depth_buffer_bit);          gltranslatef(screen_w/2,0,0);         glrotatef(0.5,0,1,0);         gltranslatef(-screen_w/2,0,0);           glpushmatrix();         gltranslatef(screen_w/2,screen_h/2,0);           glcolor3f(0.5,0.5,0);         gldrawarrays(gl_triangles, 0, vdata.size());          glpopmatrix();           sdl_gl_swapwindow(win);          sdl_delay(10);     }     sdl_destroywindow(win);     sdl_quit();     return 0; }

the stlparser methods getndata() , getvdata() have following signatures:

const std::vector<std::array<float,3>>& getndata() const; const std::vector<std::array<std::array<float,3>,3>>& getvdata() const;

stlparser output should correct, can provide sources if needed.

what doing wrong?

you should change

gldrawarrays(gl_triangles, 0, vdata.size());

to

gldrawarrays(gl_triangles, 0, 3 * vdata.size());

i.e. count should vertex count, not triangle count.


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