iOS images in a bubble effect

Question

I have some images that I want to \"put inside a bubble\". The bubbles kind of float around the screen with these images trapped inside them.

The best is a way to c

Answer 1

For the record, I ended up using GPUImage like @BradLarson suggested but I had to write a custom filter as below. This filter takes an "inside" image and a bubble texture and blends the two while also performing the refraction calculation but not inverting the image coordinates. The effect:

.h

@interface GPUImageBubbleFilter : GPUImageTwoInputFilter

@property (readwrite, nonatomic) CGFloat refractiveIndex;   
@property (readwrite, nonatomic) CGFloat radius;            

@end

.m

#import "GPUImageBubbleFilter.h"

NSString *const kGPUImageBubbleShaderString = SHADER_STRING
(
 varying highp vec2 textureCoordinate;
 varying highp vec2 textureCoordinate2;

 uniform sampler2D inputImageTexture;
 uniform sampler2D inputImageTexture2;

 uniform highp vec2 center;
 uniform highp float radius;
 uniform highp float aspectRatio;
 uniform highp float refractiveIndex;

 void main()
 {
     highp vec2 textureCoordinateToUse = vec2(textureCoordinate.x, (textureCoordinate.y * aspectRatio + 0.5 - 0.5 * aspectRatio));
     highp float distanceFromCenter = distance(center, textureCoordinateToUse);
     lowp float checkForPresenceWithinSphere = step(distanceFromCenter, radius);

     distanceFromCenter = distanceFromCenter / radius;

     highp float normalizedDepth = radius * sqrt(1.0 - distanceFromCenter * distanceFromCenter);
     highp vec3 sphereNormal = normalize(vec3(textureCoordinateToUse - center, normalizedDepth));

     highp vec3 refractedVector = refract(vec3(0.0, 0.0, -1.0), sphereNormal, refractiveIndex);

     lowp vec4 textureColor = texture2D(inputImageTexture, (refractedVector.xy + 1.0) * 0.5) * checkForPresenceWithinSphere; 
     lowp vec4 textureColor2 = texture2D(inputImageTexture2, textureCoordinate2) * checkForPresenceWithinSphere;

     gl_FragColor = mix(textureColor, textureColor2, textureColor2.a);    
 }

 );


@interface GPUImageBubbleFilter () {
    GLint radiusUniform, centerUniform, aspectRatioUniform, refractiveIndexUniform;
}

@property (readwrite, nonatomic) CGFloat aspectRatio;

@end

@implementation GPUImageBubbleFilter
@synthesize radius = _radius, refractiveIndex = _refractiveIndex, aspectRatio = _aspectRatio;

- (id) init {
    self = [super initWithFragmentShaderFromString: kGPUImageBubbleShaderString];
    if( self ) {
        radiusUniform = [filterProgram uniformIndex: @"radius"];
        aspectRatioUniform = [filterProgram uniformIndex: @"aspectRatio"];
        centerUniform = [filterProgram uniformIndex: @"center"];
        refractiveIndexUniform = [filterProgram uniformIndex: @"refractiveIndex"];

        self.radius = 0.5;
        self.refractiveIndex = 0.5;
        self.aspectRatio = 1.0;

        GLfloat center[2] = {0.5, 0.5};
        [GPUImageOpenGLESContext useImageProcessingContext];
        [filterProgram use];
        glUniform2fv(centerUniform, 1, center);

        [self setBackgroundColorRed: 0 green: 0 blue: 0 alpha: 0];
    }

    return self;
}

#pragma mark - Accessors
- (void) setRadius:(CGFloat)radius {
    _radius = radius;

    [GPUImageOpenGLESContext useImageProcessingContext];
    [filterProgram use];
    glUniform1f(radiusUniform, _radius);
}

- (void) setAspectRatio:(CGFloat)aspectRatio {
    _aspectRatio = aspectRatio;

    [GPUImageOpenGLESContext useImageProcessingContext];
    [filterProgram use];
    glUniform1f(aspectRatioUniform, _aspectRatio);
}

- (void)setRefractiveIndex:(CGFloat)newValue;
{
    _refractiveIndex = newValue;

    [GPUImageOpenGLESContext useImageProcessingContext];
    [filterProgram use];
    glUniform1f(refractiveIndexUniform, _refractiveIndex);
}

Answer 2

You can do this using the GPUImageSphereRefractionFilter from my open source GPUImage framework:

I describe in detail how this works in this answer to a question about a similar affect on Android. Basically, I use a fragment shader to refract the light that passes through an imaginary sphere, then I use that to do a lookup into a texture containing the source image. The background is blurred using a simple Gaussian blur.

If you want to achieve the exact look of the image you show, you might need to tweak this fragment shader to add some grazing-angle color to the sphere, but this should get you fairly close.

For the fun of it, I decided to try to more closely replicate the glass sphere above. I added grazing angle lighting and a specular lighting reflection on the sphere, as well as not inverting the refracted texture coordinates, leading to this result:

I used the following fragment shader for this newer version:

 varying highp vec2 textureCoordinate;

 uniform sampler2D inputImageTexture;

 uniform highp vec2 center;
 uniform highp float radius;
 uniform highp float aspectRatio;
 uniform highp float refractiveIndex;
// uniform vec3 lightPosition;
 const highp vec3 lightPosition = vec3(-0.5, 0.5, 1.0);
 const highp vec3 ambientLightPosition = vec3(0.0, 0.0, 1.0);

 void main()
 {
     highp vec2 textureCoordinateToUse = vec2(textureCoordinate.x, (textureCoordinate.y * aspectRatio + 0.5 - 0.5 * aspectRatio));
     highp float distanceFromCenter = distance(center, textureCoordinateToUse);
     lowp float checkForPresenceWithinSphere = step(distanceFromCenter, radius);

     distanceFromCenter = distanceFromCenter / radius;

     highp float normalizedDepth = radius * sqrt(1.0 - distanceFromCenter * distanceFromCenter);
     highp vec3 sphereNormal = normalize(vec3(textureCoordinateToUse - center, normalizedDepth));

     highp vec3 refractedVector = 2.0 * refract(vec3(0.0, 0.0, -1.0), sphereNormal, refractiveIndex);
     refractedVector.xy = -refractedVector.xy;

     highp vec3 finalSphereColor = texture2D(inputImageTexture, (refractedVector.xy + 1.0) * 0.5).rgb;

     // Grazing angle lighting
     highp float lightingIntensity = 2.5 * (1.0 - pow(clamp(dot(ambientLightPosition, sphereNormal), 0.0, 1.0), 0.25));
     finalSphereColor += lightingIntensity;

     // Specular lighting
     lightingIntensity  = clamp(dot(normalize(lightPosition), sphereNormal), 0.0, 1.0);
     lightingIntensity  = pow(lightingIntensity, 15.0);
     finalSphereColor += vec3(0.8, 0.8, 0.8) * lightingIntensity;

     gl_FragColor = vec4(finalSphereColor, 1.0) * checkForPresenceWithinSphere;
 }

and this filter can be run using a GPUImageGlassSphereFilter.