fix some possible div zero bugs

src/main/java/bdv/jogl/VolumeRenderer/ShaderPrograms/ShaderSources/MultiVolumeRendererShaderSource.java

@@ -151,7 +151,8 @@ public class MultiVolumeRendererShaderSource extends AbstractShaderSource{
 				"#version "+getShaderLanguageVersion(),
 				"#line "+Thread.currentThread().getStackTrace()[1].getLineNumber(),
 				"",
-				"const int "+scvMaxNumberOfVolumes+" = "+maxNumberOfVolumes+";",
+				"const int "+scvMaxNumberOfVolumes+" = "+maxNumberOfVolumes+";",	
+				"const float "+scvMinDelta+" = 0.00001;",
 				"",
 				"uniform mat4x4 "+suvViewMatrix+";",
 				"uniform mat4x4 "+suvProjectionMatrix+";",
@@ -169,7 +170,7 @@ public class MultiVolumeRendererShaderSource extends AbstractShaderSource{
 				"	vec4 positionInGlobalSpace = "+suvDrawCubeTransformation+" * position4d;",
 				"",
 				"	gl_Position ="+suvProjectionMatrix+" * "+suvViewMatrix+"  * positionInGlobalSpace;",
-				"	"+svRayStartCoordinate+"= positionInGlobalSpace.xyz /positionInGlobalSpace.w;",
+				"	"+svRayStartCoordinate+"= positionInGlobalSpace.xyz /max(positionInGlobalSpace.w,"+scvMinDelta+");",
 				"}",
 
 		};
@@ -221,7 +222,7 @@ public class MultiVolumeRendererShaderSource extends AbstractShaderSource{
 				"",
 				"vec3 getCoordinateInVolumeSpace(vec3 positionOnRay, int volumeNumber){",
 				"	vec4 transformedPosition ="+suvTextureTransformationInverse+"[volumeNumber]*vec4(positionOnRay.xyz,1.0); ",
-				"	transformedPosition /= transformedPosition.w;",
+				"	transformedPosition /= max(transformedPosition.w,"+scvMinDelta+");",
 				"	return transformedPosition.xyz;",
 				"}",
 				"",
@@ -343,7 +344,7 @@ public class MultiVolumeRendererShaderSource extends AbstractShaderSource{
 				"	"+sgvRayPositions+" = "+svRayStartCoordinate+";",	
 				"	for(int n = 0; n < "+scvMaxNumberOfVolumes+"; n++){",
 				"		vec3 tmp = "+suvVoxelCount+"[n];",
-				"	    vtextOffsets[n] = vec3(1.0/(2.0*tmp));",
+				"	    vtextOffsets[n] = vec3(1.0/(2.0*max(tmp,vec3(1.0))));",
 				"	    vtextScales[n] = (vec3("+suvVoxelCount+"[n]-ivec3(1)))/max((vec3("+suvVoxelCount+"[n])*vec3("+suvVoxelCount+"[n]-ivec3(1))),vec3(1.0));",
 				"",   
 				"	}",