Merge pull request #36031 from zxcvdev/fix_gpu_particles_some_devices

Fix undefined behavior with atan in GPU Particles

scene/resources/particles_material.cpp

@@ -316,14 +316,17 @@ void ParticlesMaterial::_update_shader() {
 
 	if (flags[FLAG_DISABLE_Z]) {
 
-		code += "		float angle1_rad = atan(direction.y, direction.x) + rand_from_seed_m1_p1(alt_seed) * spread_rad;\n";
+		code += "		float angle1_rad = rand_from_seed_m1_p1(alt_seed) * spread_rad;\n";
+		code += "		angle1_rad += direction.x != 0.0 ? atan(direction.y, direction.x) : sign(direction.y) * (pi / 2.0);\n";
 		code += "		vec3 rot = vec3(cos(angle1_rad), sin(angle1_rad), 0.0);\n";
 		code += "		VELOCITY = rot * initial_linear_velocity * mix(1.0, rand_from_seed(alt_seed), initial_linear_velocity_random);\n";
 
 	} else {
 		//initiate velocity spread in 3D
-		code += "		float angle1_rad = atan(direction.x, direction.z) + rand_from_seed_m1_p1(alt_seed) * spread_rad;\n";
-		code += "		float angle2_rad = atan(direction.y, abs(direction.z)) + rand_from_seed_m1_p1(alt_seed) * spread_rad * (1.0 - flatness);\n";
+		code += "		float angle1_rad = rand_from_seed_m1_p1(alt_seed) * spread_rad;\n";
+		code += "		float angle2_rad = rand_from_seed_m1_p1(alt_seed) * spread_rad * (1.0 - flatness);\n";
+		code += "		angle1_rad += direction.z != 0.0 ? atan(direction.x, direction.z) : sign(direction.x) * (pi / 2.0);\n";
+		code += "		angle2_rad += direction.z != 0.0 ? atan(direction.y, abs(direction.z)) : (direction.x != 0.0 ? atan(direction.y, abs(direction.x)) : sign(direction.y) * (pi / 2.0));\n";
 		code += "		vec3 direction_xz = vec3(sin(angle1_rad), 0.0, cos(angle1_rad));\n";
 		code += "		vec3 direction_yz = vec3(0.0, sin(angle2_rad), cos(angle2_rad));\n";
 		code += "		direction_yz.z = direction_yz.z / max(0.0001,sqrt(abs(direction_yz.z))); // better uniform distribution\n";