tilt-shift-camera/app/src/main/res/raw/tiltshift_fragment.glsl

#extension GL_OES_EGL_image_external : require

// Fragment shader for tilt-shift effect
// Applies gradient blur based on distance from focus line

precision mediump float;

// Camera texture (external texture for camera preview)
uniform samplerExternalOES uTexture;

// Effect parameters
uniform float uAngle;           // Rotation angle in radians
uniform float uPositionX;       // Horizontal center of focus (0-1)
uniform float uPositionY;       // Vertical center of focus (0-1)
uniform float uSize;            // Size of in-focus region (0-1)
uniform float uBlurAmount;      // Maximum blur intensity (0-1)
uniform vec2 uResolution;       // Texture resolution for proper sampling

varying vec2 vTexCoord;

// Calculate signed distance from the focus line
float focusDistance(vec2 uv) {
    // Center point of the focus region
    vec2 center = vec2(uPositionX, uPositionY);
    vec2 offset = uv - center;

    float cosA = cos(uAngle);
    float sinA = sin(uAngle);

    // After rotation, measure perpendicular distance from center line
    float rotatedY = -offset.x * sinA + offset.y * cosA;

    return abs(rotatedY);
}

// Calculate blur factor based on distance from focus
float blurFactor(float dist) {
    // Smooth transition from in-focus to blurred
    float halfSize = uSize * 0.5;
    float transitionSize = halfSize * 0.5;

    if (dist < halfSize) {
        return 0.0;  // In focus region
    }

    // Smooth falloff using smoothstep
    float normalizedDist = (dist - halfSize) / transitionSize;
    return smoothstep(0.0, 1.0, normalizedDist) * uBlurAmount;
}

// Get Gaussian weight for blur kernel (9-tap, sigma ~= 2.0)
float getWeight(int i) {
    if (i == 0) return 0.0162;
    if (i == 1) return 0.0540;
    if (i == 2) return 0.1216;
    if (i == 3) return 0.1933;
    if (i == 4) return 0.2258;
    if (i == 5) return 0.1933;
    if (i == 6) return 0.1216;
    if (i == 7) return 0.0540;
    return 0.0162; // i == 8
}

// Sample with Gaussian blur
vec4 sampleBlurred(vec2 uv, float blur) {
    if (blur < 0.01) {
        return texture2D(uTexture, uv);
    }

    vec4 color = vec4(0.0);
    vec2 texelSize = 1.0 / uResolution;

    // Blur direction perpendicular to focus line
    float blurAngle = uAngle + 1.5707963; // +90 degrees
    vec2 blurDir = vec2(cos(blurAngle), sin(blurAngle));

    // Scale blur radius by blur amount
    float radius = blur * 20.0;

    // 9-tap Gaussian blur
    for (int i = 0; i < 9; i++) {
        float offset = float(i) - 4.0;
        vec2 samplePos = uv + blurDir * texelSize * offset * radius;
        color += texture2D(uTexture, samplePos) * getWeight(i);
    }

    return color;
}

void main() {
    float dist = focusDistance(vTexCoord);
    float blur = blurFactor(dist);

    gl_FragColor = sampleBlurred(vTexCoord, blur);
}