[Metaballs] Do all the texture generation in the fragment shader

Metaballs/Renderer.swift

@@ -86,22 +86,29 @@ class Renderer: NSObject, MTKViewDelegate {
             Vertex(position: Point(x:  1, y:  1), textureCoordinate: Point(x: 1, y: 1))
         ]
 
-        let buffer = commandQueue.makeCommandBuffer()
-        buffer.label = "Compute + Render"
-
         do {
-            let _ = try field.computeEncoderForSamplingKernel(withDevice: device, commandBuffer: buffer)
+            try field.updateBuffers()
         } catch let e {
-            print("\(e)")
+            NSLog("Error updating buffers: \(e)")
         }
 
+        let buffer = commandQueue.makeCommandBuffer()
+        buffer.label = "Render"
+
+//        do {
+//            let _ = try field.computeEncoderForSamplingKernel(withDevice: device, commandBuffer: buffer)
+//        } catch let e {
+//            print("\(e)")
+//        }
+
         if let renderPass = view.currentRenderPassDescriptor {
             let encoder = buffer.makeRenderCommandEncoder(descriptor: renderPass)
             encoder.label = "Render Pass"
             encoder.setViewport(MTLViewport(originX: 0.0, originY: 0.0, width: Double(view.drawableSize.width), height: Double(view.drawableSize.height), znear: -1.0, zfar: 1.0))
             encoder.setRenderPipelineState(renderPipelineState)
-            encoder.setVertexBytes(points, length: points.count * MemoryLayout<Vertex>.size, at: 0)
-            encoder.setFragmentTexture(field.sampleTexture, at: 0)
+            encoder.setVertexBytes(points, length: points.count * MemoryLayout<Vertex>.stride, at: 0)
+            encoder.setFragmentBuffer(field.parametersBuffer, offset: 0, at: 0)
+            encoder.setFragmentBuffer(field.ballBuffer, offset: 0, at: 1)
             encoder.drawPrimitives(type: .triangle, vertexStart: 0, vertexCount: 6)
             encoder.endEncoding()
 

Metaballs/Shaders.metal

@@ -24,6 +24,13 @@ typedef struct {
     float2 textureCoordinate;
 } RasterizerData;
 
+typedef struct {
+    int2 size;
+    int numberOfBalls;
+} Parameters;
+
+typedef half3 Ball;
+
 vertex RasterizerData
 passthroughVertexShader(uint vid                    [[vertex_id]],
                         constant Vertex* vertexes   [[buffer(0)]])
@@ -35,19 +42,36 @@ passthroughVertexShader(uint vid                    [[vertex_id]],
     return out;
 }
 
+float sampleAtPoint(float2, constant Ball*, uint);
+
 fragment float4
-sampleToColorShader(RasterizerData in           [[stage_in]],
-                    texture2d<half> samples     [[texture(0)]])
+sampleToColorShader(RasterizerData in               [[stage_in]],
+                    constant Parameters& parameters [[buffer(0)]],
+                    constant Ball* balls            [[buffer(1)]])
 {
-    constexpr sampler textureSampler(mag_filter::linear, min_filter::linear);
-    const half4 sample = samples.sample(textureSampler, in.textureCoordinate);
+    const float sample = sampleAtPoint(in.textureCoordinate, balls, parameters.numberOfBalls);
 
     float4 out;
-    if (sample.r > 1.0) {
+    if (sample > 1.0) {
         out = float4(0.0, 1.0, 0.0, 0.0);
-    }
-    else {
+    } else {
         out = float4(0.0, 0.0, 0.0, 0.0);
     }
     return out;
 }
+
+float
+sampleAtPoint(float2 point,
+              constant Ball* balls,
+              uint count)
+{
+    float sample = 0.0;
+    for (uint i = 0; i < count; i++) {
+        constant Ball& ball = balls[i];
+        float r2 = ball.z * ball.z;     // Radius stored in z coordinate.
+        float xDiff = point.x - ball.x;
+        float yDiff = point.y - ball.y;
+        sample += r2 / ((xDiff * xDiff) + (yDiff * yDiff));
+    }
+    return sample;
+}