Opengl ES draw wireframe over GL_TRIANGLES correctly - opengl

Question

I need to draw a wireframe around a cube,I have everything made but I have some problem with the alpha testing, whatever I do the GL_LINES keep either overlapping the GL_TRIANGLES when they dont have to(they are behind them) or the GL_TRIANGLES keep overlapping the GL_LINES (when the lines should be visible).
Gdx.gl.glBlendFunc(GL20.GL_SRC_ALPHA, GL20.GL_ONE_MINUS_SRC_ALPHA);
Gdx.gl.glEnable(GL20.GL_DEPTH_TEST);
SquareMap.get().shader.getShader().begin();
SquareMap.get().shader.getShader().setUniformMatrix(u,camera.combined);
LineRenderer3D.get().render(SquareMap.get().shader,worldrenderer.getCamera());
TriangleRenderer3D.get().render(SquareMap.get().shader,worldrenderer.getCamera());
SquareMap.get().shader.getShader().end();
Also the wireframe is a little bigger than the cube.
The TriangleRenderer3D.get().render and LineRenderer3D().render just load the vertices and call gl_drawarrays
By enabling depth mask the cube GL_TRIANGLES overlap the lines
Do I need to enable something that I missing here?

Answer 1

It is worth mentioning that line primitives have different pixel coverage rules than triangles. A line must cross through a diamond-shaped pattern in the center of a pixel to be visible, where as a triangle needs to cover the top-left corner. This documentation is for Direct3D, but it does an infinitely better job describing these rules (which are the same in GL) than any OpenGL documentation I have come across.
As for fixing this problem, a small offset applied to all vertex positions in order to better align their centers is the most common approach. This is typically done by translating X and Y by 0.375 units.
Another Microsoft document explains this as well.
While some of the issues described in the first paragraph may be primitive coverage related, none are in the last paragraph.
The issue described in the final paragraphs can be addressed this way:
//
// Write wires wherever the line's depth is less than or equal to the triangles.
//
glDepthFunc (GL_LEQUAL);
TriangleRenderer3D.get().render(SquareMap.get().shader,worldrenderer.getCamera());
LineRenderer3D.get().render(SquareMap.get().shader,worldrenderer.getCamera());
By rendering the triangles first, and then only drawing the lines where they are either in front of or at the same depth as (default depth test discards this scenario) you should get the behavior you want. Leave depth writes enabled.