VolumeShader single quotes to double quotes

examples/js/shaders/VolumeShader.js

@@ -16,309 +16,309 @@ THREE.VolumeRenderShader1 = {
 		"u_cmdata": { value: null }
 	},
 	vertexShader: [
-		'		varying vec4 v_nearpos;',
-		'		varying vec4 v_farpos;',
-		'		varying vec3 v_position;',
-
-		'		mat4 inversemat(mat4 m) {',
-						// Taken from https://github.com/stackgl/glsl-inverse/blob/master/index.glsl
-						// This function is licenced by the MIT license to Mikola Lysenko
-		'				float',
-		'				a00 = m[0][0], a01 = m[0][1], a02 = m[0][2], a03 = m[0][3],',
-		'				a10 = m[1][0], a11 = m[1][1], a12 = m[1][2], a13 = m[1][3],',
-		'				a20 = m[2][0], a21 = m[2][1], a22 = m[2][2], a23 = m[2][3],',
-		'				a30 = m[3][0], a31 = m[3][1], a32 = m[3][2], a33 = m[3][3],',
-
-		'				b00 = a00 * a11 - a01 * a10,',
-		'				b01 = a00 * a12 - a02 * a10,',
-		'				b02 = a00 * a13 - a03 * a10,',
-		'				b03 = a01 * a12 - a02 * a11,',
-		'				b04 = a01 * a13 - a03 * a11,',
-		'				b05 = a02 * a13 - a03 * a12,',
-		'				b06 = a20 * a31 - a21 * a30,',
-		'				b07 = a20 * a32 - a22 * a30,',
-		'				b08 = a20 * a33 - a23 * a30,',
-		'				b09 = a21 * a32 - a22 * a31,',
-		'				b10 = a21 * a33 - a23 * a31,',
-		'				b11 = a22 * a33 - a23 * a32,',
-
-		'				det = b00 * b11 - b01 * b10 + b02 * b09 + b03 * b08 - b04 * b07 + b05 * b06;',
-
-		'		return mat4(',
-		'				a11 * b11 - a12 * b10 + a13 * b09,',
-		'				a02 * b10 - a01 * b11 - a03 * b09,',
-		'				a31 * b05 - a32 * b04 + a33 * b03,',
-		'				a22 * b04 - a21 * b05 - a23 * b03,',
-		'				a12 * b08 - a10 * b11 - a13 * b07,',
-		'				a00 * b11 - a02 * b08 + a03 * b07,',
-		'				a32 * b02 - a30 * b05 - a33 * b01,',
-		'				a20 * b05 - a22 * b02 + a23 * b01,',
-		'				a10 * b10 - a11 * b08 + a13 * b06,',
-		'				a01 * b08 - a00 * b10 - a03 * b06,',
-		'				a30 * b04 - a31 * b02 + a33 * b00,',
-		'				a21 * b02 - a20 * b04 - a23 * b00,',
-		'				a11 * b07 - a10 * b09 - a12 * b06,',
-		'				a00 * b09 - a01 * b07 + a02 * b06,',
-		'				a31 * b01 - a30 * b03 - a32 * b00,',
-		'				a20 * b03 - a21 * b01 + a22 * b00) / det;',
-		'		}',
-
-
-		'		void main() {',
-						// Prepare transforms to map to "camera view". See also:
-						// https://threejs.org/docs/#api/renderers/webgl/WebGLProgram
-		'				mat4 viewtransformf = viewMatrix;',
-		'				mat4 viewtransformi = inversemat(viewMatrix);',
-
-						// Project local vertex coordinate to camera position. Then do a step
-						// backward (in cam coords) to the near clipping plane, and project back. Do
-						// the same for the far clipping plane. This gives us all the information we
-						// need to calculate the ray and truncate it to the viewing cone.
-		'				vec4 position4 = vec4(position, 1.0);',
-		'				vec4 pos_in_cam = viewtransformf * position4;',
-
-						// Intersection of ray and near clipping plane (z = -1 in clip coords)
-		'				pos_in_cam.z = -pos_in_cam.w;',
-		'				v_nearpos = viewtransformi * pos_in_cam;',
-
-						// Intersection of ray and far clipping plane (z = +1 in clip coords)
-		'				pos_in_cam.z = pos_in_cam.w;',
-		'				v_farpos = viewtransformi * pos_in_cam;',
-
-						// Set varyings and output pos
-		'				v_position = position;',
-		'				gl_Position = projectionMatrix * viewMatrix * modelMatrix * position4;',
-		'		}',
-	].join( '\n' ),
+		"		varying vec4 v_nearpos;",
+		"		varying vec4 v_farpos;",
+		"		varying vec3 v_position;",
+
+		"		mat4 inversemat(mat4 m) {",
+		// Taken from https://github.com/stackgl/glsl-inverse/blob/master/index.glsl
+		// This function is licenced by the MIT license to Mikola Lysenko
+		"				float",
+		"				a00 = m[0][0], a01 = m[0][1], a02 = m[0][2], a03 = m[0][3],",
+		"				a10 = m[1][0], a11 = m[1][1], a12 = m[1][2], a13 = m[1][3],",
+		"				a20 = m[2][0], a21 = m[2][1], a22 = m[2][2], a23 = m[2][3],",
+		"				a30 = m[3][0], a31 = m[3][1], a32 = m[3][2], a33 = m[3][3],",
+
+		"				b00 = a00 * a11 - a01 * a10,",
+		"				b01 = a00 * a12 - a02 * a10,",
+		"				b02 = a00 * a13 - a03 * a10,",
+		"				b03 = a01 * a12 - a02 * a11,",
+		"				b04 = a01 * a13 - a03 * a11,",
+		"				b05 = a02 * a13 - a03 * a12,",
+		"				b06 = a20 * a31 - a21 * a30,",
+		"				b07 = a20 * a32 - a22 * a30,",
+		"				b08 = a20 * a33 - a23 * a30,",
+		"				b09 = a21 * a32 - a22 * a31,",
+		"				b10 = a21 * a33 - a23 * a31,",
+		"				b11 = a22 * a33 - a23 * a32,",
+
+		"				det = b00 * b11 - b01 * b10 + b02 * b09 + b03 * b08 - b04 * b07 + b05 * b06;",
+
+		"		return mat4(",
+		"				a11 * b11 - a12 * b10 + a13 * b09,",
+		"				a02 * b10 - a01 * b11 - a03 * b09,",
+		"				a31 * b05 - a32 * b04 + a33 * b03,",
+		"				a22 * b04 - a21 * b05 - a23 * b03,",
+		"				a12 * b08 - a10 * b11 - a13 * b07,",
+		"				a00 * b11 - a02 * b08 + a03 * b07,",
+		"				a32 * b02 - a30 * b05 - a33 * b01,",
+		"				a20 * b05 - a22 * b02 + a23 * b01,",
+		"				a10 * b10 - a11 * b08 + a13 * b06,",
+		"				a01 * b08 - a00 * b10 - a03 * b06,",
+		"				a30 * b04 - a31 * b02 + a33 * b00,",
+		"				a21 * b02 - a20 * b04 - a23 * b00,",
+		"				a11 * b07 - a10 * b09 - a12 * b06,",
+		"				a00 * b09 - a01 * b07 + a02 * b06,",
+		"				a31 * b01 - a30 * b03 - a32 * b00,",
+		"				a20 * b03 - a21 * b01 + a22 * b00) / det;",
+		"		}",
+
+
+		"		void main() {",
+		// Prepare transforms to map to "camera view". See also:
+		// https://threejs.org/docs/#api/renderers/webgl/WebGLProgram
+		"				mat4 viewtransformf = viewMatrix;",
+		"				mat4 viewtransformi = inversemat(viewMatrix);",
+
+		// Project local vertex coordinate to camera position. Then do a step
+		// backward (in cam coords) to the near clipping plane, and project back. Do
+		// the same for the far clipping plane. This gives us all the information we
+		// need to calculate the ray and truncate it to the viewing cone.
+		"				vec4 position4 = vec4(position, 1.0);",
+		"				vec4 pos_in_cam = viewtransformf * position4;",
+
+		// Intersection of ray and near clipping plane (z = -1 in clip coords)
+		"				pos_in_cam.z = -pos_in_cam.w;",
+		"				v_nearpos = viewtransformi * pos_in_cam;",
+
+		// Intersection of ray and far clipping plane (z = +1 in clip coords)
+		"				pos_in_cam.z = pos_in_cam.w;",
+		"				v_farpos = viewtransformi * pos_in_cam;",
+
+		// Set varyings and output pos
+		"				v_position = position;",
+		"				gl_Position = projectionMatrix * viewMatrix * modelMatrix * position4;",
+		"		}",
+	].join( "\n" ),
 	fragmentShader: [
-		'		precision highp float;',
-		'		precision mediump sampler3D;',
-
-		'		uniform vec3 u_size;',
-		'		uniform int u_renderstyle;',
-		'		uniform float u_renderthreshold;',
-		'		uniform vec2 u_clim;',
-
-		'		uniform sampler3D u_data;',
-		'		uniform sampler2D u_cmdata;',
-
-		'		varying vec3 v_position;',
-		'		varying vec4 v_nearpos;',
-		'		varying vec4 v_farpos;',
-
-				// The maximum distance through our rendering volume is sqrt(3).
-		'		const int MAX_STEPS = 887;	// 887 for 512^3, 1774 for 1024^3',
-		'		const int REFINEMENT_STEPS = 4;',
-		'		const float relative_step_size = 1.0;',
-		'		const vec4 ambient_color = vec4(0.2, 0.4, 0.2, 1.0);',
-		'		const vec4 diffuse_color = vec4(0.8, 0.2, 0.2, 1.0);',
-		'		const vec4 specular_color = vec4(1.0, 1.0, 1.0, 1.0);',
-		'		const float shininess = 40.0;',
-
-		'		void cast_mip(vec3 start_loc, vec3 step, int nsteps, vec3 view_ray);',
-		'		void cast_iso(vec3 start_loc, vec3 step, int nsteps, vec3 view_ray);',
-
-		'		float sample1(vec3 texcoords);',
-		'		vec4 apply_colormap(float val);',
-		'		vec4 add_lighting(float val, vec3 loc, vec3 step, vec3 view_ray);',
-
-
-		'		void main() {',
-						// Normalize clipping plane info
-		'				vec3 farpos = v_farpos.xyz / v_farpos.w;',
-		'				vec3 nearpos = v_nearpos.xyz / v_nearpos.w;',
-
-						// Calculate unit vector pointing in the view direction through this fragment.
-		'				vec3 view_ray = normalize(nearpos.xyz - farpos.xyz);',
-
-						// Compute the (negative) distance to the front surface or near clipping plane.
-						// v_position is the back face of the cuboid, so the initial distance calculated in the dot
-						// product below is the distance from near clip plane to the back of the cuboid
-		'				float distance = dot(nearpos - v_position, view_ray);',
-		'				distance = max(distance, min((-0.5 - v_position.x) / view_ray.x,',
-		'																		(u_size.x - 0.5 - v_position.x) / view_ray.x));',
-		'				distance = max(distance, min((-0.5 - v_position.y) / view_ray.y,',
-		'																		(u_size.y - 0.5 - v_position.y) / view_ray.y));',
-		'				distance = max(distance, min((-0.5 - v_position.z) / view_ray.z,',
-		'																		(u_size.z - 0.5 - v_position.z) / view_ray.z));',
-
-																				// Now we have the starting position on the front surface
-		'				vec3 front = v_position + view_ray * distance;',
-
-						// Decide how many steps to take
-		'				int nsteps = int(-distance / relative_step_size + 0.5);',
-		'				if ( nsteps < 1 )',
-		'						discard;',
-
-						// Get starting location and step vector in texture coordinates
-		'				vec3 step = ((v_position - front) / u_size) / float(nsteps);',
-		'				vec3 start_loc = front / u_size;',
-
-						// For testing: show the number of steps. This helps to establish
-						// whether the rays are correctly oriented
-						//'gl_FragColor = vec4(0.0, float(nsteps) / 1.0 / u_size.x, 1.0, 1.0);',
-						//'return;',
-
-		'				if (u_renderstyle == 0)',
-		'						cast_mip(start_loc, step, nsteps, view_ray);',
-		'				else if (u_renderstyle == 1)',
-		'						cast_iso(start_loc, step, nsteps, view_ray);',
-
-		'				if (gl_FragColor.a < 0.05)',
-		'						discard;',
-		'		}',
-
-
-		'		float sample1(vec3 texcoords) {',
-		'				/* Sample float value from a 3D texture. Assumes intensity data. */',
-		'				return texture(u_data, texcoords.xyz).r;',
-		'		}',
-
-
-		'		vec4 apply_colormap(float val) {',
-		'				val = (val - u_clim[0]) / (u_clim[1] - u_clim[0]);',
-		'				return texture2D(u_cmdata, vec2(val, 0.5));',
-		'		}',
-
-
-		'		void cast_mip(vec3 start_loc, vec3 step, int nsteps, vec3 view_ray) {',
-
-		'				float max_val = -1e6;',
-		'				int max_i = 100;',
-		'				vec3 loc = start_loc;',
-
-						// Enter the raycasting loop. In WebGL 1 the loop index cannot be compared with
-						// non-constant expression. So we use a hard-coded max, and an additional condition
-						// inside the loop.
-		'				for (int iter=0; iter<MAX_STEPS; iter++) {',
-		'						if (iter >= nsteps)',
-		'								break;',
-								// Sample from the 3D texture
-		'						float val = sample1(loc);',
-								// Apply MIP operation
-		'						if (val > max_val) {',
-		'								max_val = val;',
-		'								max_i = iter;',
-		'						}',
-								// Advance location deeper into the volume
-		'						loc += step;',
-		'				}',
-
-						// Refine location, gives crispier images
-		'				vec3 iloc = start_loc + step * (float(max_i) - 0.5);',
-		'				vec3 istep = step / float(REFINEMENT_STEPS);',
-		'				for (int i=0; i<REFINEMENT_STEPS; i++) {',
-		'						max_val = max(max_val, sample1(iloc));',
-		'						iloc += istep;',
-		'				}',
-
-						// Resolve final color
-		'				gl_FragColor = apply_colormap(max_val);',
-		'		}',
-
-
-		'		void cast_iso(vec3 start_loc, vec3 step, int nsteps, vec3 view_ray) {',
-
-		'				gl_FragColor = vec4(0.0);	// init transparent',
-		'				vec4 color3 = vec4(0.0);	// final color',
-		'				vec3 dstep = 1.5 / u_size;	// step to sample derivative',
-		'				vec3 loc = start_loc;',
-
-		'				float low_threshold = u_renderthreshold - 0.02 * (u_clim[1] - u_clim[0]);',
-
-						// Enter the raycasting loop. In WebGL 1 the loop index cannot be compared with
-						// non-constant expression. So we use a hard-coded max, and an additional condition
-						// inside the loop.
-		'				for (int iter=0; iter<MAX_STEPS; iter++) {',
-		'						if (iter >= nsteps)',
-		'								break;',
-
-										// Sample from the 3D texture
-		'						float val = sample1(loc);',
-
-		'						if (val > low_threshold) {',
-								// Take the last interval in smaller steps
-		'								vec3 iloc = loc - 0.5 * step;',
-		'								vec3 istep = step / float(REFINEMENT_STEPS);',
-		'								for (int i=0; i<REFINEMENT_STEPS; i++) {',
-		'										val = sample1(iloc);',
-		'										if (val > u_renderthreshold) {',
-		'												gl_FragColor = add_lighting(val, iloc, dstep, view_ray);',
-		'												return;',
-		'										}',
-		'										iloc += istep;',
-		'								}',
-		'						}',
-
-								// Advance location deeper into the volume
-		'						loc += step;',
-		'				}',
-		'		}',
-
-
-		'		vec4 add_lighting(float val, vec3 loc, vec3 step, vec3 view_ray)',
-		'		{',
-						// Calculate color by incorporating lighting
-
-						// View direction
-		'				vec3 V = normalize(view_ray);',
-
-						// calculate normal vector from gradient
-		'				vec3 N;',
-		'				float val1, val2;',
-		'				val1 = sample1(loc + vec3(-step[0], 0.0, 0.0));',
-		'				val2 = sample1(loc + vec3(+step[0], 0.0, 0.0));',
-		'				N[0] = val1 - val2;',
-		'				val = max(max(val1, val2), val);',
-		'				val1 = sample1(loc + vec3(0.0, -step[1], 0.0));',
-		'				val2 = sample1(loc + vec3(0.0, +step[1], 0.0));',
-		'				N[1] = val1 - val2;',
-		'				val = max(max(val1, val2), val);',
-		'				val1 = sample1(loc + vec3(0.0, 0.0, -step[2]));',
-		'				val2 = sample1(loc + vec3(0.0, 0.0, +step[2]));',
-		'				N[2] = val1 - val2;',
-		'				val = max(max(val1, val2), val);',
-
-		'				float gm = length(N); // gradient magnitude',
-		'				N = normalize(N);',
-
-						// Flip normal so it points towards viewer
-		'				float Nselect = float(dot(N, V) > 0.0);',
-		'				N = (2.0 * Nselect - 1.0) * N;	// ==	Nselect * N - (1.0-Nselect)*N;',
-
-						// Init colors
-		'				vec4 ambient_color = vec4(0.0, 0.0, 0.0, 0.0);',
-		'				vec4 diffuse_color = vec4(0.0, 0.0, 0.0, 0.0);',
-		'				vec4 specular_color = vec4(0.0, 0.0, 0.0, 0.0);',
-
-						// note: could allow multiple lights
-		'				for (int i=0; i<1; i++)',
-		'				{',
+		"		precision highp float;",
+		"		precision mediump sampler3D;",
+
+		"		uniform vec3 u_size;",
+		"		uniform int u_renderstyle;",
+		"		uniform float u_renderthreshold;",
+		"		uniform vec2 u_clim;",
+
+		"		uniform sampler3D u_data;",
+		"		uniform sampler2D u_cmdata;",
+
+		"		varying vec3 v_position;",
+		"		varying vec4 v_nearpos;",
+		"		varying vec4 v_farpos;",
+
+		// The maximum distance through our rendering volume is sqrt(3).
+		"		const int MAX_STEPS = 887;	// 887 for 512^3, 1774 for 1024^3",
+		"		const int REFINEMENT_STEPS = 4;",
+		"		const float relative_step_size = 1.0;",
+		"		const vec4 ambient_color = vec4(0.2, 0.4, 0.2, 1.0);",
+		"		const vec4 diffuse_color = vec4(0.8, 0.2, 0.2, 1.0);",
+		"		const vec4 specular_color = vec4(1.0, 1.0, 1.0, 1.0);",
+		"		const float shininess = 40.0;",
+
+		"		void cast_mip(vec3 start_loc, vec3 step, int nsteps, vec3 view_ray);",
+		"		void cast_iso(vec3 start_loc, vec3 step, int nsteps, vec3 view_ray);",
+
+		"		float sample1(vec3 texcoords);",
+		"		vec4 apply_colormap(float val);",
+		"		vec4 add_lighting(float val, vec3 loc, vec3 step, vec3 view_ray);",
+
+
+		"		void main() {",
+		// Normalize clipping plane info
+		"				vec3 farpos = v_farpos.xyz / v_farpos.w;",
+		"				vec3 nearpos = v_nearpos.xyz / v_nearpos.w;",
+
+		// Calculate unit vector pointing in the view direction through this fragment.
+		"				vec3 view_ray = normalize(nearpos.xyz - farpos.xyz);",
+
+		// Compute the (negative) distance to the front surface or near clipping plane.
+		// v_position is the back face of the cuboid, so the initial distance calculated in the dot
+		// product below is the distance from near clip plane to the back of the cuboid
+		"				float distance = dot(nearpos - v_position, view_ray);",
+		"				distance = max(distance, min((-0.5 - v_position.x) / view_ray.x,",
+		"																		(u_size.x - 0.5 - v_position.x) / view_ray.x));",
+		"				distance = max(distance, min((-0.5 - v_position.y) / view_ray.y,",
+		"																		(u_size.y - 0.5 - v_position.y) / view_ray.y));",
+		"				distance = max(distance, min((-0.5 - v_position.z) / view_ray.z,",
+		"																		(u_size.z - 0.5 - v_position.z) / view_ray.z));",
+
+		// Now we have the starting position on the front surface
+		"				vec3 front = v_position + view_ray * distance;",
+
+		// Decide how many steps to take
+		"				int nsteps = int(-distance / relative_step_size + 0.5);",
+		"				if ( nsteps < 1 )",
+		"						discard;",
+
+		// Get starting location and step vector in texture coordinates
+		"				vec3 step = ((v_position - front) / u_size) / float(nsteps);",
+		"				vec3 start_loc = front / u_size;",
+
+		// For testing: show the number of steps. This helps to establish
+		// whether the rays are correctly oriented
+		//'gl_FragColor = vec4(0.0, float(nsteps) / 1.0 / u_size.x, 1.0, 1.0);',
+		//'return;',
+
+		"				if (u_renderstyle == 0)",
+		"						cast_mip(start_loc, step, nsteps, view_ray);",
+		"				else if (u_renderstyle == 1)",
+		"						cast_iso(start_loc, step, nsteps, view_ray);",
+
+		"				if (gl_FragColor.a < 0.05)",
+		"						discard;",
+		"		}",
+
+
+		"		float sample1(vec3 texcoords) {",
+		"				/* Sample float value from a 3D texture. Assumes intensity data. */",
+		"				return texture(u_data, texcoords.xyz).r;",
+		"		}",
+
+
+		"		vec4 apply_colormap(float val) {",
+		"				val = (val - u_clim[0]) / (u_clim[1] - u_clim[0]);",
+		"				return texture2D(u_cmdata, vec2(val, 0.5));",
+		"		}",
+
+
+		"		void cast_mip(vec3 start_loc, vec3 step, int nsteps, vec3 view_ray) {",
+
+		"				float max_val = -1e6;",
+		"				int max_i = 100;",
+		"				vec3 loc = start_loc;",
+
+		// Enter the raycasting loop. In WebGL 1 the loop index cannot be compared with
+		// non-constant expression. So we use a hard-coded max, and an additional condition
+		// inside the loop.
+		"				for (int iter=0; iter<MAX_STEPS; iter++) {",
+		"						if (iter >= nsteps)",
+		"								break;",
+		// Sample from the 3D texture
+		"						float val = sample1(loc);",
+		// Apply MIP operation
+		"						if (val > max_val) {",
+		"								max_val = val;",
+		"								max_i = iter;",
+		"						}",
+		// Advance location deeper into the volume
+		"						loc += step;",
+		"				}",
+
+		// Refine location, gives crispier images
+		"				vec3 iloc = start_loc + step * (float(max_i) - 0.5);",
+		"				vec3 istep = step / float(REFINEMENT_STEPS);",
+		"				for (int i=0; i<REFINEMENT_STEPS; i++) {",
+		"						max_val = max(max_val, sample1(iloc));",
+		"						iloc += istep;",
+		"				}",
+
+		// Resolve final color
+		"				gl_FragColor = apply_colormap(max_val);",
+		"		}",
+
+
+		"		void cast_iso(vec3 start_loc, vec3 step, int nsteps, vec3 view_ray) {",
+
+		"				gl_FragColor = vec4(0.0);	// init transparent",
+		"				vec4 color3 = vec4(0.0);	// final color",
+		"				vec3 dstep = 1.5 / u_size;	// step to sample derivative",
+		"				vec3 loc = start_loc;",
+
+		"				float low_threshold = u_renderthreshold - 0.02 * (u_clim[1] - u_clim[0]);",
+
+		// Enter the raycasting loop. In WebGL 1 the loop index cannot be compared with
+		// non-constant expression. So we use a hard-coded max, and an additional condition
+		// inside the loop.
+		"				for (int iter=0; iter<MAX_STEPS; iter++) {",
+		"						if (iter >= nsteps)",
+		"								break;",
+
+		// Sample from the 3D texture
+		"						float val = sample1(loc);",
+
+		"						if (val > low_threshold) {",
+		// Take the last interval in smaller steps
+		"								vec3 iloc = loc - 0.5 * step;",
+		"								vec3 istep = step / float(REFINEMENT_STEPS);",
+		"								for (int i=0; i<REFINEMENT_STEPS; i++) {",
+		"										val = sample1(iloc);",
+		"										if (val > u_renderthreshold) {",
+		"												gl_FragColor = add_lighting(val, iloc, dstep, view_ray);",
+		"												return;",
+		"										}",
+		"										iloc += istep;",
+		"								}",
+		"						}",
+
+		// Advance location deeper into the volume
+		"						loc += step;",
+		"				}",
+		"		}",
+
+
+		"		vec4 add_lighting(float val, vec3 loc, vec3 step, vec3 view_ray)",
+		"		{",
+		// Calculate color by incorporating lighting
+
+		// View direction
+		"				vec3 V = normalize(view_ray);",
+
+		// calculate normal vector from gradient
+		"				vec3 N;",
+		"				float val1, val2;",
+		"				val1 = sample1(loc + vec3(-step[0], 0.0, 0.0));",
+		"				val2 = sample1(loc + vec3(+step[0], 0.0, 0.0));",
+		"				N[0] = val1 - val2;",
+		"				val = max(max(val1, val2), val);",
+		"				val1 = sample1(loc + vec3(0.0, -step[1], 0.0));",
+		"				val2 = sample1(loc + vec3(0.0, +step[1], 0.0));",
+		"				N[1] = val1 - val2;",
+		"				val = max(max(val1, val2), val);",
+		"				val1 = sample1(loc + vec3(0.0, 0.0, -step[2]));",
+		"				val2 = sample1(loc + vec3(0.0, 0.0, +step[2]));",
+		"				N[2] = val1 - val2;",
+		"				val = max(max(val1, val2), val);",
+
+		"				float gm = length(N); // gradient magnitude",
+		"				N = normalize(N);",
+
+		// Flip normal so it points towards viewer
+		"				float Nselect = float(dot(N, V) > 0.0);",
+		"				N = (2.0 * Nselect - 1.0) * N;	// ==	Nselect * N - (1.0-Nselect)*N;",
+
+		// Init colors
+		"				vec4 ambient_color = vec4(0.0, 0.0, 0.0, 0.0);",
+		"				vec4 diffuse_color = vec4(0.0, 0.0, 0.0, 0.0);",
+		"				vec4 specular_color = vec4(0.0, 0.0, 0.0, 0.0);",
+
+		// note: could allow multiple lights
+		"				for (int i=0; i<1; i++)",
+		"				{",
 								 // Get light direction (make sure to prevent zero devision)
-		'						vec3 L = normalize(view_ray);	//lightDirs[i];',
-		'						float lightEnabled = float( length(L) > 0.0 );',
-		'						L = normalize(L + (1.0 - lightEnabled));',
-
-								// Calculate lighting properties
-		'						float lambertTerm = clamp(dot(N, L), 0.0, 1.0);',
-		'						vec3 H = normalize(L+V); // Halfway vector',
-		'						float specularTerm = pow(max(dot(H, N), 0.0), shininess);',
-
-								// Calculate mask
-		'						float mask1 = lightEnabled;',
-
-								// Calculate colors
-		'						ambient_color +=	mask1 * ambient_color;	// * gl_LightSource[i].ambient;',
-		'						diffuse_color +=	mask1 * lambertTerm;',
-		'						specular_color += mask1 * specularTerm * specular_color;',
-		'				}',
-
-						// Calculate final color by componing different components
-		'				vec4 final_color;',
-		'				vec4 color = apply_colormap(val);',
-		'				final_color = color * (ambient_color + diffuse_color) + specular_color;',
-		'				final_color.a = color.a;',
-		'				return final_color;',
-		'		}',
-	].join( '\n' )
+		"						vec3 L = normalize(view_ray);	//lightDirs[i];",
+		"						float lightEnabled = float( length(L) > 0.0 );",
+		"						L = normalize(L + (1.0 - lightEnabled));",
+
+		// Calculate lighting properties
+		"						float lambertTerm = clamp(dot(N, L), 0.0, 1.0);",
+		"						vec3 H = normalize(L+V); // Halfway vector",
+		"						float specularTerm = pow(max(dot(H, N), 0.0), shininess);",
+
+		// Calculate mask
+		"						float mask1 = lightEnabled;",
+
+		// Calculate colors
+		"						ambient_color +=	mask1 * ambient_color;	// * gl_LightSource[i].ambient;",
+		"						diffuse_color +=	mask1 * lambertTerm;",
+		"						specular_color += mask1 * specularTerm * specular_color;",
+		"				}",
+
+		// Calculate final color by componing different components
+		"				vec4 final_color;",
+		"				vec4 color = apply_colormap(val);",
+		"				final_color = color * (ambient_color + diffuse_color) + specular_color;",
+		"				final_color.a = color.a;",
+		"				return final_color;",
+		"		}",
+	].join( "\n" )
 };