[rshapes] Horizontal and Vertical Lines Starting at {0, 0} Not Drawing in Raylib

[evanz2608]

Please, before submitting a new issue verify and check:

• I tested it on latest raylib version from master branch
• I checked there is no similar issue already reported
• I checked the documentation on the wiki
• My code has no errors or misuse of raylib

Issue description

Hi, while trying to draw horizontal lines i found that the line starting at {0, 0} does not get drawn. Same issue if i tried to draw vertical line.

Environment

Platform: DESKTOP
OS: Arch linux
INFO: GL: OpenGL device information:
INFO: > Vendor: AMD
INFO: > Renderer: AMD Radeon RX 570 Series (radeonsi, polaris10, LLVM 17.0.6, DRM 3.57, 6.9.5-arch1-1)
INFO: > Version: 4.6 (Core Profile) Mesa 24.1.1-arch1.1
INFO: > GLSL: 4.60

Issue Screenshot

Code Example

#include <raylib.h>

int main() {
  int width = 800;
  int height = 600;
  int row_size = height / 10;

  InitWindow(width, height, "Title");

  while (!WindowShouldClose()) {
    BeginDrawing();

    ClearBackground(DARKBLUE);

    for (int y = 0; y <= row_size; ++y) {
      DrawLine(0, y * row_size, width, y * row_size, WHITE);
    }

    EndDrawing();
  }
  CloseWindow();
}

[raysan5]

@evanz2608 I verified this issue, it is highly dependant on GPU and drivers. The logic to draw the line it's following the expected OpenGL specs but drivers decided it's out of screen and should be culled, already reviewed that function several times but every new update breaks something else.

I'll try to revert to previous implementation, using QUADS instead of LINES, that seemed to work for most cases, except this #3884

Related issues:

• [rshapes] Line drawing bug when using Camera2D #4075
• [rshape] Line drawing functions are no longer pixel-perfect #3973
• [rshapes] Off-by-one difference between DrawRectangleLinesEx and DrawLine/DrawLineV at drawing position. #3931
• [rshapes] DrawRectangleLines() lines flickering when zooming out due to RL_LINES vs RL_QUADS  #3884

[evanz2608]

@raysan5 Ohh i see, thx for the response! Closing the issue then.

[raysan5]

@evanz2608 Reopening it! Actually the issue has not been addressed yet! Indeed drawing a line at 0,0 must work! 😄

[evanz2608]

First of all, sorry for my bad english, i will try to explain myself the best i can.
I think i found what the problem is. Because i tried to use 0 as Y coordinate in both start and end point of the line, the gpu never draw the line because it never passes through the center of any pixel. If i pass startPosY=1 and endPosY=1, then the line are drawn into the first pixel row of the window. Use DrawPixelV instead and adding 0.5 to each component of the vector solves the problem.

[raysan5]

Issue addressed by proposed PR, discussion can continue there...