[Blender 2.8x] Add option to set OpenGL point size for particle debugging

[PavelBlend]

System Information

Blender Version (including hash): 2.81 (sub 16), branch: master, commit date: 2019-12-04 11:32, hash: rBf1aa4d18d49d
FLIP Fluids Version: 1.0.7
Operating System: Windows 7 64 bit
CPU: AMD A8 5600K
GFX: -
RAM: 8 GB

Describe the bug

Particle Size (Debug Panel) has disappeared in Blender 2.81.

Expected Behaviour

You can do it as follows:
bgl.glPointSize(particle_size)

Actual Behaviour

There is no way to specify the particle size.

[rlguy]

Hi PavelBlend,

Thanks for the report! We had to remove the option to set pointsize for Blender 2.8x. The addon uses the new Blender 2.8x drawing system which uses the gpu module that uses vertex and fragment shaders instead of the old bgl module. As far as I could find, there is not a way to specify the point size in the gpu module.

Here is a code snippet of the shaders that we're using in Blender 2.8x:

vertex_shader = """
    uniform mat4 ModelViewProjectionMatrix;
    uniform float pointsize;

    in vec3 pos;
    in vec4 color;

    out vec4 finalColor;

    void main()
    {
        gl_PointSize = pointsize;
        gl_Position = ModelViewProjectionMatrix * vec4(pos, 1.0);
        finalColor = color;
    }
"""

fragment_shader = """
    in vec4 finalColor;
    out vec4 fragColor;

    void main()
    {
        fragColor = finalColor;
    }
"""

particle_shader = gpu.types.GPUShader(vertex_shader, fragment_shader)
particle_shader.uniform_float('pointsize', dprops.debug.particle_size)
particle_batch_draw = batch_for_shader(
    particle_shader, 'POINTS',
    {"pos": particle_vertices, "color": particle_vertex_colors},
)

We are setting the OpenGL pointsize in the shader with gl_PointSize = pointsize;. But this does not seem to affect how it is actually drawn in the Blender viewport when changing the size. I had posted a questions about this on the Blender Artists forums, but did not receive an answer. I may need to try the https://devtalk.blender.org/ forum to ask the developers why this does not work.

[PavelBlend]

Everything works in my jet fluids addon:
https://github.com/PavelBlend/blender_jet_fluids_addon/blob/master/jet_fluids/render.py#L48
I ported it to blender 2.80.
Despite the fact that I am using the gpu module, I still specify the size of the points using the bgl module:

[rlguy]

Thank you so much for the tip! This fixes the problem. I did not know the bgl module would work like this.

I have added this fix to the addon. If you would like to add this fix to your installation, unzip the following file:

issue_484_patch.zip

And replace the scripts at these locations:

• flip_fluids_addon/ui/domain_debug_ui.py
• flip_fluids_addon/operators/draw_operators.py