Initial commit

shaders/trail.gdshader

@@ -2,7 +2,16 @@ shader_type particles;
 
 render_mode keep_data,disable_force,disable_velocity;
 
+uniform vec3 acceleration = vec3(0,1,0);
 
+const float fixed_dt = 1.0/60.0;
+void simulate(inout vec3 pos0, inout vec3 vel0, inout vec3 pos1, inout vec3 vel1, float dt) {
+	vel0 += acceleration * dt;
+	vel1 += acceleration * dt;
+
+	pos0 += vel0 * dt;
+	pos1 += vel1 * dt;
+}
 
 void process() {
 	// CUSTOM.w tracks the particles place in the trail, in range (0..LIFETIME]
@@ -21,22 +30,38 @@ void process() {
 
 		// needed to initialize in case of CUSTOM.w == 2.0
 		TRANSFORM = mat4(a,a,b,b);
+		VELOCITY = vec3(0);
+		COLOR.xyz = vec3(0);
 	}
 
+	vec3 pos0 = (TRANSFORM[0] + TRANSFORM[3]).xyz/2.0;
+	vec3 pos1 = (TRANSFORM[1] + TRANSFORM[2]).xyz/2.0;
+	vec3 d0 = pos0;
+	vec3 d1 = pos1;
+	simulate(pos0,VELOCITY,pos1,COLOR.xyz,DELTA);
+	TRANSFORM[0].xyz += pos0 - d0;
+	TRANSFORM[3].xyz += pos0 - d0;
+	TRANSFORM[1].xyz += pos1 - d1;
+	TRANSFORM[2].xyz += pos1 - d1;
+
 	// restart
 	if(CUSTOM.w == amount+1.0){
 		CUSTOM.w = 1.0;
 	}
-	
+
 	if(CUSTOM.w == 1.0){
 		// sets the quad to the line to cache this frame, it is not yet visible
 		TRANSFORM = mat4(a,a,b,b);
+		VELOCITY = vec3(0);
+		COLOR.xyz = vec3(0);
 	}
 
 	if(CUSTOM.w == 2.0){
 		// sets the right edge of the quad
 		TRANSFORM[1] = a;
 		TRANSFORM[2] = b;
+
+		COLOR.xyz = vec3(0);
 	}
 
 	CUSTOM.w++;