V0.1.4, added Floyd Steinberg algorithm and revisited UI

Sources/iDither/ContentView.swift

@@ -9,7 +9,7 @@ struct ContentView: View {
     var body: some View {
         NavigationSplitView {
             SidebarView(viewModel: viewModel, isImporting: $isImporting, isExporting: $isExporting)
-                .navigationSplitViewColumnWidth(min: 260, ideal: 300)
+                .navigationSplitViewColumnWidth(min: 280, ideal: 300)
         } detail: {
             DetailView(viewModel: viewModel, loadFromProviders: loadFromProviders)
         }
@@ -100,66 +100,115 @@ struct SidebarView: View {
     @Binding var isExporting: Bool
     
     var body: some View {
-        Form {
+        ScrollView {
-            Section("Dithering Algorithm") {
+            VStack(alignment: .leading, spacing: 16) {
+                
+                // --- ALGORITHM SECTION ---
+                VStack(alignment: .leading, spacing: 12) {
+                    Text("ALGORITHM")
+                        .font(.system(size: 11, weight: .medium))
+                        .foregroundStyle(.secondary)
+                        .padding(.top, 8)
+                    
                     Picker("Algorithm", selection: $viewModel.selectedAlgorithm) {
                         ForEach(DitherAlgorithm.allCases) { algo in
                             Text(algo.name).tag(algo)
                         }
                     }
+                    .labelsHidden() // Native look: just the dropdown
                     
                     Toggle("Grayscale / 1-bit", isOn: $viewModel.isGrayscale)
+                        .toggleStyle(.switch)
+                        .padding(.top, 4)
                 }
                 
-            Section("Pre-Processing") {
+                Divider()
-                VStack(alignment: .leading) {
+                    .padding(.vertical, 8)
+                
+                // --- PRE-PROCESSING SECTION ---
+                VStack(alignment: .leading, spacing: 16) {
+                    Text("PRE-PROCESSING")
+                        .font(.system(size: 11, weight: .medium))
+                        .foregroundStyle(.secondary)
+                    
+                    // Brightness slider
+                    VStack(spacing: 6) {
                         HStack {
                             Text("Brightness")
+                                .font(.system(size: 13))
                             Spacer()
                             Text(String(format: "%.2f", viewModel.brightness))
-                            .monospacedDigit()
+                                .font(.system(size: 13, weight: .medium))
                                 .foregroundStyle(.secondary)
+                                .monospacedDigit()
                         }
                         Slider(value: $viewModel.brightness, in: -1.0...1.0)
+                            .tint(.accentColor)
                     }
                     
-                VStack(alignment: .leading) {
+                    // Contrast slider
+                    VStack(spacing: 6) {
                         HStack {
                             Text("Contrast")
+                                .font(.system(size: 13))
                             Spacer()
                             Text(String(format: "%.2f", viewModel.contrast))
-                            .monospacedDigit()
+                                .font(.system(size: 13, weight: .medium))
                                 .foregroundStyle(.secondary)
+                                .monospacedDigit()
                         }
                         Slider(value: $viewModel.contrast, in: 0.0...4.0)
+                            .tint(.accentColor)
                     }
                     
-                VStack(alignment: .leading) {
+                    // Pixel Scale slider
+                    VStack(spacing: 6) {
                         HStack {
                             Text("Pixel Scale")
+                                .font(.system(size: 13))
                             Spacer()
                             Text("\(Int(viewModel.pixelScale))x")
-                            .monospacedDigit()
+                                .font(.system(size: 13, weight: .medium))
                                 .foregroundStyle(.secondary)
+                                .monospacedDigit()
                         }
                         Slider(value: $viewModel.pixelScale, in: 1.0...20.0, step: 1.0)
+                            .tint(.accentColor)
+                    }
                 }
                 
-                VStack(alignment: .leading) {
+                Divider()
+                    .padding(.vertical, 8)
+                
+                // --- QUANTIZATION SECTION ---
+                VStack(alignment: .leading, spacing: 16) {
+                    Text("QUANTIZATION")
+                        .font(.system(size: 11, weight: .medium))
+                        .foregroundStyle(.secondary)
+                    
+                    VStack(spacing: 6) {
                         HStack {
                             Text("Color Depth")
+                                .font(.system(size: 13))
                             Spacer()
                             Text("\(Int(viewModel.colorDepth))")
-                            .monospacedDigit()
+                                .font(.system(size: 13, weight: .medium))
                                 .foregroundStyle(.secondary)
+                                .monospacedDigit()
                         }
                         Slider(value: $viewModel.colorDepth, in: 1.0...32.0, step: 1.0)
+                            .tint(.accentColor)
                     }
                 }
+                
+                Spacer()
             }
-        .formStyle(.grouped)
+            .padding(20)
-        .padding(.vertical)
+        }
+        .background(.regularMaterial) // Native material background
+        .ignoresSafeArea(edges: .top) // Fix for titlebar gap
         .navigationTitle("iDither")
+        .frame(minWidth: 280, maxWidth: .infinity, alignment: .leading)
         .toolbar {
             ToolbarItemGroup(placement: .primaryAction) {
                 Button(action: { isImporting = true }) {

Sources/iDither/Renderer/MetalImageRenderer.swift

@@ -15,6 +15,8 @@ final class MetalImageRenderer: Sendable {
     private let device: MTLDevice
     private let commandQueue: MTLCommandQueue
     private let pipelineState: MTLComputePipelineState
+    private let pipelineStateFS_Pass1: MTLComputePipelineState?
+    private let pipelineStateFS_Pass2: MTLComputePipelineState?
     
     init?() {
         guard let device = MTLCreateSystemDefaultDevice(),
@@ -29,6 +31,15 @@ final class MetalImageRenderer: Sendable {
         
         do {
             self.pipelineState = try device.makeComputePipelineState(function: function)
+            // Load FS Kernels
+            if let f1 = library.makeFunction(name: "ditherShaderFS_Pass1"),
+               let f2 = library.makeFunction(name: "ditherShaderFS_Pass2") {
+                self.pipelineStateFS_Pass1 = try device.makeComputePipelineState(function: f1)
+                self.pipelineStateFS_Pass2 = try device.makeComputePipelineState(function: f2)
+            } else {
+                self.pipelineStateFS_Pass1 = nil
+                self.pipelineStateFS_Pass2 = nil
+            }
         } catch {
             print("Failed to create pipeline state: \(error)")
             return nil
@@ -60,11 +71,53 @@ final class MetalImageRenderer: Sendable {
             return nil
         }
         
+        var params = params
+        
+        if params.algorithm == 7, let pipe1 = pipelineStateFS_Pass1, let pipe2 = pipelineStateFS_Pass2 {
+            // FLOYD-STEINBERG MULTI-PASS
+            
+            // Create Error Texture (Float16 or Float32 for precision)
+            let errorDesc = MTLTextureDescriptor.texture2DDescriptor(pixelFormat: .rgba16Float,
+                                                                     width: inputTexture.width,
+                                                                     height: inputTexture.height,
+                                                                     mipmapped: false)
+            errorDesc.usage = [.shaderWrite, .shaderRead]
+            guard let errorTexture = device.makeTexture(descriptor: errorDesc) else {
+                 computeEncoder.endEncoding()
+                 return nil
+            }
+            
+            // PASS 1: Even Rows
+            computeEncoder.setComputePipelineState(pipe1)
+            computeEncoder.setTexture(inputTexture, index: 0)
+            computeEncoder.setTexture(outputTexture, index: 1)
+            computeEncoder.setTexture(errorTexture, index: 2)
+            computeEncoder.setBytes(&params, length: MemoryLayout<RenderParameters>.stride, index: 0)
+            
+            // Dispatch (1, H/2, 1) -> Each thread handles one full row
+            let h = (inputTexture.height + 1) / 2
+            let threadsPerGrid = MTLSizeMake(1, h, 1)
+            let threadsPerThreadgroup = MTLSizeMake(1, min(h, pipe1.maxTotalThreadsPerThreadgroup), 1)
+            
+            computeEncoder.dispatchThreads(threadsPerGrid, threadsPerThreadgroup: threadsPerThreadgroup)
+            
+            // Memory Barrier (Ensure Pass 1 writes are visible to Pass 2)
+            computeEncoder.memoryBarrier(scope: .textures)
+            
+            // PASS 2: Odd Rows
+            computeEncoder.setComputePipelineState(pipe2)
+            computeEncoder.setTexture(inputTexture, index: 0)
+            computeEncoder.setTexture(outputTexture, index: 1)
+            computeEncoder.setTexture(errorTexture, index: 2)
+            computeEncoder.setBytes(&params, length: MemoryLayout<RenderParameters>.stride, index: 0)
+            
+            computeEncoder.dispatchThreads(threadsPerGrid, threadsPerThreadgroup: threadsPerThreadgroup)
+            
+        } else {
+            // STANDARD ALGORITHMS
             computeEncoder.setComputePipelineState(pipelineState)
             computeEncoder.setTexture(inputTexture, index: 0)
             computeEncoder.setTexture(outputTexture, index: 1)
-        
-        var params = params
             computeEncoder.setBytes(&params, length: MemoryLayout<RenderParameters>.stride, index: 0)
             
             let w = pipelineState.threadExecutionWidth
@@ -73,13 +126,13 @@ final class MetalImageRenderer: Sendable {
             let threadsPerGrid = MTLSizeMake(inputTexture.width, inputTexture.height, 1)
             
             computeEncoder.dispatchThreads(threadsPerGrid, threadsPerThreadgroup: threadsPerThreadgroup)
+        }
+
         computeEncoder.endEncoding()
         
         commandBuffer.commit()
         commandBuffer.waitUntilCompleted()
         
-        // Convert back to CGImage (for simplicity in this iteration, though MTKView is better for display)
-        // We will use a helper to convert MTLTexture to CGImage
         return createCGImage(from: outputTexture)
     }
     

Sources/iDither/Resources/Shaders.metal

@@ -165,5 +165,211 @@ kernel void ditherShader(texture2d<float, access::read> inputTexture [[texture(0
         }
     }
     
+
     outputTexture.write(float4(rgb, color.a), gid);
 }
+
+// ==================================================================================
+// FLOYD-STEINBERG ERROR DIFFUSION HELPERS & KERNELS (Algorithm ID 7)
+// ==================================================================================
+
+// Helper to get luminance for error calculation in grayscale mode
+float getLuma(float3 rgb) {
+    return dot(rgb, float3(0.299, 0.587, 0.114));
+}
+
+// PASS 1: EVEN ROWS (Left -> Right)
+// - Reads original pixel
+// - Dithers it
+// - Writes result to outputTexture
+// - Writes RAW error 'diff' to errorTexture (at current coord) for Pass 2 to consume
+kernel void ditherShaderFS_Pass1(texture2d<float, access::read> inputTexture [[texture(0)]],
+                                 texture2d<float, access::write> outputTexture [[texture(1)]],
+                                 texture2d<float, access::write> errorTexture [[texture(2)]],
+                                 constant RenderParameters &params [[buffer(0)]],
+                                 uint2 gid [[thread_position_in_grid]]) {
+    
+    // Dispatch: (1, height/2, 1). Each thread processes one FULL ROW.
+    uint y = gid.y * 2; // Pass 1 processes EVEN rows: 0, 2, 4...
+    
+    if (y >= inputTexture.get_height()) return;
+    
+    uint width = inputTexture.get_width();
+    float3 currentError = float3(0.0); // Error propagated from immediate Left neighbor
+    
+    // Scale handling (minimal implementation for now, usually FS runs 1:1)
+    // If pixel scale > 1, FS behaves weirdly unless we downsample/upsample.
+    // For now, let's treat FS as operating on the native coordinates (or scaled ones).
+    // The previous shader code did manual pixelation.
+    // To support `pixelScale`, we simply use the scaled coordinates for reading input,
+    // but we iterate 1:1 on output? No, if we pixelate, we want blocky dither?
+    // FS is hard to 'blocky' dither without pre-scaling.
+    // Let's stick to 1:1 processing for the error diffusion logic itself.
+    // But we read the input color from the "pixelated" coordinate.
+    
+    float scale = max(1.0, params.pixelScale);
+    
+    for (uint x = 0; x < width; x++) {
+        uint2 coords = uint2(x, y);
+        
+        // Pixelate Input Read
+        uint2 mappedCoords = uint2(floor(float(x) / scale) * scale, floor(float(y) / scale) * scale);
+        mappedCoords.x = min(mappedCoords.x, inputTexture.get_width() - 1);
+        mappedCoords.y = min(mappedCoords.y, inputTexture.get_height() - 1);
+
+        float4 colorRaw = inputTexture.read(mappedCoords);
+        float3 originalColor = colorRaw.rgb;
+        
+        // Color Adjust
+        originalColor = originalColor + params.brightness;
+        originalColor = (originalColor - 0.5) * params.contrast + 0.5;
+        
+        // Grayscale
+        if (params.isGrayscale > 0) {
+            float l = getLuma(originalColor);
+            originalColor = float3(l);
+        }
+        
+        // ----------------------------------------------------
+        // ERROR DIFFUSION CORE
+        // ----------------------------------------------------
+        
+        // Add error from Left Neighbor (Pass 1 is L->R)
+        float3 pixelIn = originalColor + currentError;
+        
+        // Quantize
+        float3 pixelOut = float3(0.0);
+        float levels = max(1.0, params.colorDepth); // Ensure no div by zero
+        if (levels <= 1.0) levels = 2.0;
+
+        pixelOut.r = floor(pixelIn.r * (levels - 1.0) + 0.5) / (levels - 1.0);
+        pixelOut.g = floor(pixelIn.g * (levels - 1.0) + 0.5) / (levels - 1.0);
+        pixelOut.b = floor(pixelIn.b * (levels - 1.0) + 0.5) / (levels - 1.0);
+        
+        pixelOut = clamp(pixelOut, 0.0, 1.0);
+        
+        // Calculate Error
+        float3 diff = pixelIn - pixelOut;
+        
+        // Store RAW error for Pass 2 (Row below) to read
+        // Note: we store 'diff', NOT the distributed parts. Pass 2 will calculate distribution.
+        if (y + 1 < inputTexture.get_height()) {
+            errorTexture.write(float4(diff, 1.0), coords);
+        }
+        
+        outputTexture.write(float4(pixelOut, colorRaw.a), coords);
+        
+        // Propagate to Right Neighbor (7/16)
+        currentError = diff * (7.0 / 16.0);
+    }
+}
+
+// PASS 2: ODD ROWS (Right -> Left Serpentine)
+// - Reads original pixel
+// - Absorbs error from Row Above (which stored RAW diffs)
+// - Dithers
+// - Writes result
+kernel void ditherShaderFS_Pass2(texture2d<float, access::read> inputTexture [[texture(0)]],
+                                 texture2d<float, access::write> outputTexture [[texture(1)]],
+                                 texture2d<float, access::read> errorTexture [[texture(2)]], // Contains diffs from Pass 1
+                                 constant RenderParameters &params [[buffer(0)]],
+                                 uint2 gid [[thread_position_in_grid]]) {
+    
+    // Dispatch: (1, height/2, 1)
+    uint y = gid.y * 2 + 1; // Pass 2 processes ODD rows: 1, 3, 5...
+    
+    if (y >= inputTexture.get_height()) return;
+    
+    uint width = inputTexture.get_width();
+    float3 currentError = float3(0.0); // Error propagated from immediate Right neighbor (Serpentine R->L)
+    
+    float scale = max(1.0, params.pixelScale);
+    
+    // Serpentine: Iterate Right to Left
+    for (int x_int = int(width) - 1; x_int >= 0; x_int--) {
+        uint x = uint(x_int);
+        uint2 coords = uint2(x, y);
+        
+        // 1. Calculate Incoming Error from Row Above (Even Row, L->R)
+        // Row Above is y-1. We are at x.
+        // Even Row (y-1) propagated error to us (y) via:
+        // - (x-1, y-1) sent 3/16 (Bottom Left) -> reaches ME at x if I am (x-1+1) = x. Correct.
+        // - (x,   y-1) sent 5/16 (Down)        -> reaches ME at x. Correct.
+        // - (x+1, y-1) sent 1/16 (Bottom Right)-> reaches ME at x. Correct.
+        
+        float3 errorFromAbove = float3(0.0);
+        uint prevY = y - 1;
+        
+        // Read neighbor errors (and apply weights now)
+        
+        // From Top-Left (x-1, y-1): It pushed 3/16 to Bottom-Right (x) ? No.
+        // Standard FS (Left->Right scan):
+        // P(x, y) distributes:
+        // Right (x+1, y): 7/16
+        // Bottom-Left (x-1, y+1): 3/16
+        // Bottom (x, y+1): 5/16
+        // Bottom-Right (x+1, y+1): 1/16
+        
+        // So, ME (x, y) receives from:
+        // (x+1, y-1) [Top Right]: sent 3/16 to its Bottom Left (which is ME).
+        // (x,   y-1) [Top]:       sent 5/16 to its Bottom (which is ME).
+        // (x-1, y-1) [Top Left]:  sent 1/16 to its Bottom Right (which is ME).
+        
+        // Read Top Right (x+1, prevY)
+        if (x + 1 < width) {
+            float3 e = errorTexture.read(uint2(x+1, prevY)).rgb;
+            errorFromAbove += e * (3.0 / 16.0);
+        }
+        
+        // Read Top (x, prevY)
+        {
+            float3 e = errorTexture.read(uint2(x, prevY)).rgb;
+            errorFromAbove += e * (5.0 / 16.0);
+        }
+        
+        // Read Top Left (x-1, prevY)
+        if (x >= 1) {
+            float3 e = errorTexture.read(uint2(x-1, prevY)).rgb;
+            errorFromAbove += e * (1.0 / 16.0);
+        }
+        
+        // 2. Read Pixel
+        uint2 mappedCoords = uint2(floor(float(x) / scale) * scale, floor(float(y) / scale) * scale);
+        mappedCoords.x = min(mappedCoords.x, inputTexture.get_width() - 1);
+        mappedCoords.y = min(mappedCoords.y, inputTexture.get_height() - 1);
+        
+        float4 colorRaw = inputTexture.read(mappedCoords);
+        float3 originalColor = colorRaw.rgb;
+        originalColor = originalColor + params.brightness;
+        originalColor = (originalColor - 0.5) * params.contrast + 0.5;
+        
+        if (params.isGrayscale > 0) {
+            float l = getLuma(originalColor);
+            originalColor = float3(l);
+        }
+        
+        // 3. Combine
+        float3 pixelIn = originalColor + currentError + errorFromAbove;
+        
+        // 4. Quantize
+        float3 pixelOut = float3(0.0);
+        float levels = max(1.0, params.colorDepth);
+        if (levels <= 1.0) levels = 2.0;
+
+        pixelOut.r = floor(pixelIn.r * (levels - 1.0) + 0.5) / (levels - 1.0);
+        pixelOut.g = floor(pixelIn.g * (levels - 1.0) + 0.5) / (levels - 1.0);
+        pixelOut.b = floor(pixelIn.b * (levels - 1.0) + 0.5) / (levels - 1.0);
+        pixelOut = clamp(pixelOut, 0.0, 1.0);
+        
+        // 5. Diff
+        float3 diff = pixelIn - pixelOut;
+        
+        outputTexture.write(float4(pixelOut, colorRaw.a), coords);
+        
+        // 6. Propagate Horizontally (Serpentine R->L)
+        // In R->L scan, 'Right' neighbor in FS diagram is actually 'Left' neighbor in spatial.
+        // We push 7/16 to the next pixel we visit (x-1).
+        currentError = diff * (7.0 / 16.0);
+    }
+}
+

Sources/iDither/ViewModel/DitherViewModel.swift

@@ -10,6 +10,7 @@ enum DitherAlgorithm: Int, CaseIterable, Identifiable {
     case cluster4x4 = 4
     case cluster8x8 = 5
     case blueNoise = 6
+    case floydSteinberg = 7
     
     var id: Int { rawValue }
     
@@ -22,6 +23,7 @@ enum DitherAlgorithm: Int, CaseIterable, Identifiable {
         case .cluster4x4: return "Cluster 4x4 (Vintage)"
         case .cluster8x8: return "Cluster 8x8 (Soft)"
         case .blueNoise: return "Blue Noise / Organic (Best Quality)"
+        case .floydSteinberg: return "Floyd-Steinberg (Error Diffusion)"
         }
     }
 }

Sources/iDither/iDitherApp.swift

@@ -15,6 +15,7 @@ struct iDitherApp: App {
                     }
                 }
         }
+        .windowStyle(.hiddenTitleBar)
         .windowToolbarStyle(.unified)
     }
 }