glLineWidth works incorrectly

[Archer-zty]

Thanks for the project. I have met a problem.
When I test glLineWidth(9.f) on raw glad+glfw, line width is shown as follows:

But the rotating rectangle only occupies 1 piexl in example1.cpp whatever the parameter is.
Any idea?

line 600 in example1.cpp, I change the code like this

/* Draw 2 triangles starting at index 0 */
+glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
+glLineWidth(9.f);
mShader.drawIndexed(GL_TRIANGLES, 0, 2);
+glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);

[svenevs]

I don't have a computer whose driver actually supports glLineWidth greater than 1, but as a sanity check -- does glLineWidth even apply to drawing triangles? I truly don't know, I've long since abandoned glLineWidth as it's generally poorly supported / cannot be relied on for consistent results.

If it does apply (as opposed to changing the shader to actually be lines and then mShader.drawIndexed(GL_LINES, 0, /* however many you made */);), it may be that the underlying NanoVG libraries' OpenGL state modification is interfering? Perhaps something gets disabled that you need to re-enable or vice versa?

[wjakob]

Changing line width is actually a legacy feature. AFAIK OpenGL drivers are are allowed to ignore this value, and some of the machines I work with will do so.

[svenevs]

When I test glLineWidth(9.f) on raw glad+glfw, line width is shown as follows:

@Archer-zty how exactly did you initialize the context? NanoGUI requests an OpenGL 3.3 forward compatible core profile.

Changing line width is actually a legacy feature

So if you want to go with NanoGUI but keep your linewidth stuff, I believe you cannot request forward compatible or core (meaning use the empty screen constructor, example 3 shows self-managed GLFW). You may also need to request an older profile altogether?

That said, I vaguely recall NanoVG (underlying widget library) not working if you remove those.

[Archer-zty]

@svenevs Thank you for response. I initialize the context with OpenGL 3.3 and even 4.5 but neither works in NanoGUI(However, figure 1 works).

I think I should abandon this function like @wjakob said "Changing line width is actually a legacy feature".