GhGl shader respecting lights in the scene

devin_jernigan · September 19, 2020, 4:04pm

Hi,

Could someone help me to understand how I can modify the code in the GL Mesh Shader button to respect the lights in a scene? Or am I just missing how the GL Mesh Shader works?

Thanks!

ajarindia · September 19, 2020, 4:22pm

Hi,

Resources GHGL

Cheers,
BVR

stevebaer · September 19, 2020, 7:35pm

GhGL grabs the lights in the display pipeline and sets them up as uniforms available in the shader

github.com

mcneel/ghgl/blob/master/src/BuiltIn.cs#L252


const int maxlights = 4;

Register("_lightCount", "int", "number of lights in the scene", (location, display) =>

{

    // Use reflection until 6.3 goes to release candidate. GetLights is not available until 6.3

    //var lights = display.GetLights();

    var lights = GetLightsHelper(display);

    int count = lights.Length < maxlights ? lights.Length : 4;

    OpenGL.glUniform1i(location, count);

});



Register($"_lightPosition[{maxlights}]", "vec3", "array of four light positions", (location, display) =>

{

    // Use reflection until 6.3 goes to release candidate. GetLights is not available until 6.3

    //var lights = display.GetLights();

    var lights = GetLightsHelper(display);

    float[] v = new float[3 * maxlights];

    for (int i = 0; i < lights.Length; i++)

    {

        if (i >= maxlights)

            break;

        var loc = lights[i].Location;

devin_jernigan · September 19, 2020, 7:52pm

Ok, I think I understand now. Do I just need to work within those 4 light direction options? Or is there another way to override this and tell it to use the scene lights for the lighting?

edit(2):

I was able to manipulate the direction of the lighting by creating a vector input (as an MD Slider) named lightdir and then multiplying it by the _lightDirection in the Main function in the fragment portion of the shader. I hope this helps someone else.

vec3 l = normalize(_lightDirection[0]*lightdir);

stevebaer · September 20, 2020, 5:13pm

The code in the shader needs to decide if ift is going to support more lights. I never got around to writing a sample that used more than the standard camera oriented light.

leonbrohmann · December 28, 2020, 11:43am

If have seen this thread too late. Thank you all!
At the bottom you can see a working solution in combination with a glslify lambert function -.
(With just one light source)

The changed fragment shader:

#pragma glslify: diffuse_lambert = require(‘glsl-diffuse-lambert’)

//Input variables
uniform vec4 diffuse;
uniform vec4 ambient;

uniform vec3 _lightDirection[4];

in vec3 normal;
in vec3 ligthDir;

out vec4 fragment_color;

void main() {
vec3 l = -normalize(_lightDirection[0]);
float power = diffuse_lambert(l,normal);

vec3 c = ambient.rgb + diffuse.rgb * abs(power);
vec4 shadingColor = vec4(c, diffuse.a);

fragment_color = shadingColor;
}

Now, I just would like to implement some kind of drop shadow, but as I understood, this will be right now not possible, because PostDrawObject is used to draw the object within the gl mesh shader component (GLMeshShaderComponent.cs, Line 212) - so it is too late for a shadow pass.

See this Issue;
https://mcneel.myjetbrains.com/youtrack/issue/RH-54147

@stevebaer Is this assumption correct?

Greetings,
Leon

stevebaer · January 4, 2021, 6:27pm

Yes, that is correct