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Created attachment 3984 [details]
Reset the verts pointer.

SDL_RenderDrawLine overflows the verts buffer in opengl renderer.

output of valgrind:

ATTENTION: default value of option vblank_mode overridden by environment.
==19519== Conditional jump or move depends on uninitialised value(s)
==19519==    at 0x408D282: GL_RunCommandQueue (SDL_render_gl.c:1233)
==19519==    by 0x4086BD0: FlushRenderCommands (SDL_render.c:216)
==19519==    by 0x4086BD0: SDL_RenderPresent_REAL (SDL_render.c:3089)
...

src/render/opengl/SDL_render_gl.c:
                    for (i = 0; i < count; ++i, verts += 2) {
                        data->glVertex2f(verts[0], verts[1]);
                    }
...
                    #if defined(__MACOSX__) || defined(__WIN32__)
                    /* Mac OS X and Windows seem to always leave the last point open */
                    data->glVertex2f(verts[(count-1)*2], verts[(count*2)-1]);
                    #else
                    /* Linux seems to leave the right-most or bottom-most point open */
                    x1 = verts[0];
                    y1 = verts[1];
                    x2 = verts[(count-1)*2];
                    y2 = verts[(count*2)-1];
...