StretchDistortion

framework/Source/GPUImageStretchDistortionFilter.h

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+//
+//  GPUImageStrechFilter.h
+//  Face Esplode
+
+
+#import "GPUImageFilter.h"
+
+@interface GPUImageStretchDistortionFilter : GPUImageFilter {
+    GLint centerUniform;
+}
+
+// The center about which to apply the distortion, with a default of (0.5, 0.5)
+@property(readwrite, nonatomic) CGPoint center;
+
+@end

framework/Source/GPUImageStretchDistortionFilter.m

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+//
+//  GPUImageStrechFilter.m
+
+#import "GPUImageStretchDistortionFilter.h"
+
+NSString *const kGPUImageStretchDistortionFragmentShaderString = SHADER_STRING
+(
+ varying highp vec2 textureCoordinate;
+
+ uniform sampler2D inputImageTexture;
+
+ uniform highp vec2 center;
+
+ void main()
+ {
+     highp vec2 normCoord = 2.0 * textureCoordinate - 1.0;
+     highp vec2 normCenter = 2.0 * center - 1.0;
+
+     normCoord -= normCenter;
+     mediump vec2 s = sign(normCoord);
+     normCoord = abs(normCoord);
+     normCoord = 0.5 * normCoord + 0.5 * smoothstep(0.25, 0.5, normCoord) * normCoord;
+     normCoord = s * normCoord;
+
+     normCoord += normCenter;
+
+     mediump vec2 textureCoordinateToUse = normCoord / 2.0 + 0.5;
+
+
+     gl_FragColor = texture2D(inputImageTexture, textureCoordinateToUse );
+
+ }
+ );
+
+
+@implementation GPUImageStretchDistortionFilter
+
+@synthesize center = _center;
+
+#pragma mark -
+#pragma mark Initialization and teardown
+
+- (id)init;
+{
+    if (!(self = [super initWithFragmentShaderFromString:kGPUImageStretchDistortionFragmentShaderString]))
+    {
+		return nil;
+    }
+
+    centerUniform = [filterProgram uniformIndex:@"center"];
+
+
+
+    self.center = CGPointMake(0.5, 0.5);
+
+    return self;
+}
+
+#pragma mark -
+#pragma mark Accessors
+
+
+- (void)setCenter:(CGPoint)newValue;
+{
+    _center = newValue;
+
+    [GPUImageOpenGLESContext useImageProcessingContext];
+    [filterProgram use];
+
+    GLfloat centerPosition[2];
+    centerPosition[0] = _center.x;
+    centerPosition[1] = _center.y;
+
+    glUniform2fv(centerUniform, 1, centerPosition);
+}
+
+
+@end