Shadow volume without stencil buffer

Stencil-like shadows based on alpha blending (You can create shadow-volume without Stencil-buffer operations)

This requires a complex material of 4 shaders.

This implementation includes a simple volume generator. It does not support flat-shaded models and non-closed geometry.

Tested renderers:

1.  Forward + : Most likely works on any hardware
2. Compatibility : It’s not working May work when render_priority is balanced – [-1, 0, 1, 0] (Only works on some graphics cards)
   
3. GLES 3 (Godot 3) : Works but probably depends on the hardware
4. GLES 2 : It’s not working

Tested hardware:

• [Intel HD 4000] : Forward+, Compatibility, GLES 3
• [Quadro M1000M]: Forward+, Compatibility, GLES 3
• [Radeon R5 (Stoney Ridge)]: Forward+, Compatibility, GLES 3

If you have any ideas how to run it in GLES 2 – post in comments

It looks like the Compatibility render contains bugs in the implementation, I don’t recommend using it with this technique.

It may depend on your hardware, so if you tested and it didn’t work for you, please post your hardware in the comments.

Shader code

shader_type spatial;

//render_mode unshaded, cull_front, blend_add, world_vertex_coords;
//render_mode unshaded, cull_back, blend_sub, world_vertex_coords;
//render_mode unshaded, cull_front, blend_sub, depth_test_disabled, world_vertex_coords;
//render_mode unshaded, cull_back, blend_add, depth_test_disabled, world_vertex_coords;

//For this to work, you need to create 4 materials with different render_mode and nest each one into the next_pass of the next. (Don't try to realize this, just download Demo from github and see the structure of the material)

uniform vec3 light_position;
uniform float light_radius = 50.0;

void vertex() {
	vec3 rd = VERTEX - light_position;
	vec3 rn = normalize(rd);
	if (dot(NORMAL, rn) > 0.0) {
		VERTEX += rn*clamp(light_radius-length(rd), 0.0, light_radius);
	}
	else {
		VERTEX -= NORMAL*0.01;
	}
}

void fragment() {
	ALPHA = 0.5;
}

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