verlet integration in gpu

js/simulation/GPUMath.js

@@ -116,6 +116,17 @@ define(['glBoilerplate'], function(glBoilerplate){
         this.frameBuffers[texture2Name] = temp;
     };
 
+    GPUMath.prototype.swap3Textures = function(texture1Name, texture2Name, texture3Name){
+        var temp = this.textures[texture3Name];
+        this.textures[texture3Name] = this.textures[texture2Name];
+        this.textures[texture2Name] = this.textures[texture1Name];
+        this.textures[texture1Name] = temp;
+        temp = this.frameBuffers[texture3Name];
+        this.frameBuffers[texture3Name] = this.frameBuffers[texture2Name];
+        this.frameBuffers[texture2Name] = this.frameBuffers[texture1Name];
+        this.frameBuffers[texture1Name] = temp;
+    };
+
     GPUMath.prototype.readyToRead = function(){
         return gl.checkFramebufferStatus(gl.FRAMEBUFFER) == gl.FRAMEBUFFER_COMPLETE;
     };

js/simulation/function/EM/shaders/positionCalcShader.js

@@ -3,8 +3,9 @@ precision highp float;
 uniform vec2 u_textureDim;
 uniform float u_dt;
 
-uniform sampler2D u_velocity;
+uniform sampler2D u_acceleration;
 uniform sampler2D u_lastTranslation;
+uniform sampler2D u_lastLastTranslation;
 uniform sampler2D u_mass;
 
 void main(){
@@ -18,9 +19,10 @@ void main(){
     }
 
     vec3 lastTranslation = texture2D(u_lastTranslation, scaledFragCoord).xyz;
-    vec3 velocity = texture2D(u_velocity, scaledFragCoord).xyz;
+    vec3 lastLastTranslation = texture2D(u_lastLastTranslation, scaledFragCoord).xyz;
+    vec3 acceleration = texture2D(u_acceleration, scaledFragCoord).xyz;
 
-    vec3 translation = lastTranslation + velocity*u_dt;
+    vec3 translation = 2.0*lastTranslation - lastLastTranslation + acceleration*u_dt*u_dt;
 
     gl_FragColor = vec4(translation, 0);
 }
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