OpenGL: Directional Shadow Splits debug draw mode is not implemented

[Calinou]

Godot version: Git 89a43d9

OS/device including version: Fedora 33, GeForce GTX 1080 (NVIDIA 460.39)

Issue description:

Following the removal of support for colored shadows to improve performance, the Directional Shadow Splits debug draw mode no longer works. It now displays exactly like the normal draw mode.

Back when colored shadows were supported, each split had different shadow colors thanks to this code:

godot/servers/rendering/renderer_rd/renderer_scene_render_rd.cpp

Lines 6319 to 6354 in f91c4c0

	if (get_debug_draw_mode() == RS::VIEWPORT_DEBUG_DRAW_PSSM_SPLITS) {
	light_data.shadow_color1[0] = 1.0;
	light_data.shadow_color1[1] = 0.0;
	light_data.shadow_color1[2] = 0.0;
	light_data.shadow_color1[3] = 1.0;
	light_data.shadow_color2[0] = 0.0;
	light_data.shadow_color2[1] = 1.0;
	light_data.shadow_color2[2] = 0.0;
	light_data.shadow_color2[3] = 1.0;
	light_data.shadow_color3[0] = 0.0;
	light_data.shadow_color3[1] = 0.0;
	light_data.shadow_color3[2] = 1.0;
	light_data.shadow_color3[3] = 1.0;
	light_data.shadow_color4[0] = 1.0;
	light_data.shadow_color4[1] = 1.0;
	light_data.shadow_color4[2] = 0.0;
	light_data.shadow_color4[3] = 1.0;
	} else {
	light_data.shadow_color1[0] = shadow_col.r;
	light_data.shadow_color1[1] = shadow_col.g;
	light_data.shadow_color1[2] = shadow_col.b;
	light_data.shadow_color1[3] = 1.0;
	light_data.shadow_color2[0] = shadow_col.r;
	light_data.shadow_color2[1] = shadow_col.g;
	light_data.shadow_color2[2] = shadow_col.b;
	light_data.shadow_color2[3] = 1.0;
	light_data.shadow_color3[0] = shadow_col.r;
	light_data.shadow_color3[1] = shadow_col.g;
	light_data.shadow_color3[2] = shadow_col.b;
	light_data.shadow_color3[3] = 1.0;
	light_data.shadow_color4[0] = shadow_col.r;
	light_data.shadow_color4[1] = shadow_col.g;
	light_data.shadow_color4[2] = shadow_col.b;
	light_data.shadow_color4[3] = 1.0;
	}

Speaking of which, we should also remove the shadow color property from Light3D as it's no longer effective.

Steps to reproduce:

Select Debug Advanced… > Directional Shadow Splits in the 3D viewport's Perspective menu:

Minimal reproduction project: test_debug_draw_splits.zip

[Calinou]

This was fixed in 4.2.2 or earlier in Forward+ and Mobile, but the Compatibility rendering method is still missing an implementation of this debug draw mode.