Added the ability to write to gl_FragDepth. It doesn't affect the depth prepass.

drivers/gles3/shader_compiler_gles3.cpp

@@ -872,6 +872,7 @@ ShaderCompilerGLES3::ShaderCompilerGLES3() {
 	actions[VS::SHADER_SPATIAL].renames["SCREEN_UV"] = "screen_uv";
 	actions[VS::SHADER_SPATIAL].renames["SCREEN_TEXTURE"] = "screen_texture";
 	actions[VS::SHADER_SPATIAL].renames["DEPTH_TEXTURE"] = "depth_buffer";
+	actions[VS::SHADER_SPATIAL].renames["DEPTH"] = "gl_FragDepth";
 	actions[VS::SHADER_SPATIAL].renames["ALPHA_SCISSOR"] = "alpha_scissor";
 	actions[VS::SHADER_SPATIAL].renames["OUTPUT_IS_SRGB"] = "SHADER_IS_SRGB";
 

servers/visual/shader_types.cpp

@@ -109,6 +109,7 @@ ShaderTypes::ShaderTypes() {
 	shader_modes[VS::SHADER_SPATIAL].functions["fragment"].built_ins["EMISSION"] = ShaderLanguage::TYPE_VEC3;
 	shader_modes[VS::SHADER_SPATIAL].functions["fragment"].built_ins["SCREEN_TEXTURE"] = ShaderLanguage::TYPE_SAMPLER2D;
 	shader_modes[VS::SHADER_SPATIAL].functions["fragment"].built_ins["DEPTH_TEXTURE"] = ShaderLanguage::TYPE_SAMPLER2D;
+	shader_modes[VS::SHADER_SPATIAL].functions["fragment"].built_ins["DEPTH"] = ShaderLanguage::TYPE_FLOAT;
 	shader_modes[VS::SHADER_SPATIAL].functions["fragment"].built_ins["SCREEN_UV"] = ShaderLanguage::TYPE_VEC2;
 	shader_modes[VS::SHADER_SPATIAL].functions["fragment"].built_ins["POINT_COORD"] = constt(ShaderLanguage::TYPE_VEC2);
 	shader_modes[VS::SHADER_SPATIAL].functions["fragment"].built_ins["ALPHA_SCISSOR"] = ShaderLanguage::TYPE_FLOAT;