/*
    WebGPU Example - Color Multi Sample Triangle Example
    
    GPUMultisampleState describe how a GPURenderPipeline interacts with a render pass's multisampled attachments. 
    Example uses sample count of 4
*/

const sampleCount = 4; // change from 1 to 4 to see the effect

let canvas = document.createElement('canvas');
document.body.appendChild( canvas );
canvas.width  = canvas.height = 32;

canvas.style.width  = '512px';
canvas.style.height = '512px';

const adapter = await navigator.gpu.requestAdapter();
const device  = await adapter.requestDevice();
const context = canvas.getContext('webgpu');

const presentationSize   = [ canvas.width,   
                             canvas.height ] 

const presentationFormat = navigator.gpu.getPreferredCanvasFormat();

context.configure({ device : device,
                    alphaMode: 'premultiplied', 
                    format : presentationFormat,
                    size   : presentationSize });
const vertWGSL = `
struct VSOut {
    @builtin(position) Position: vec4<f32>,
    @location(0)       color   : vec3<f32>,
};

@vertex
fn main(@location(0) inPos  : vec3<f32>,
        @location(1) inColor: vec3<f32>) -> VSOut 
{
    var vsOut: VSOut;
    vsOut.Position = vec4<f32>(inPos, 1.0);
    vsOut.color    = inColor;
    return vsOut;
}
`;

const fragWGSL = `
@fragment
fn main(@location(0) inColor: vec3<f32>) -> @location(0) vec4<f32> 
{
    return vec4<f32>(inColor, 1.0);
}
`;

const positions = new Float32Array([-1.0, -1.0, 0.0,   // Position Vertex Buffer Data
                                     1.0, -1.0, 0.0,
                                     0.0,  1.0, 0.0 ]);
const colors    = new Float32Array([ 1.0, 0.0, 0.0,    // Color Vertex Buffer Data
                                     0.0, 1.0, 0.0, 
                                     0.0, 0.0, 1.0  ]);
const indices   = new Uint16Array( [ 0, 1, 2 ]);       // Index Buffer Data

const createBuffer = (arrData, usage) => {
  const buffer = device.createBuffer({ size            : ((arrData.byteLength + 3) & ~3),
                                       usage           : usage,
                                       mappedAtCreation: true  });
  if ( arrData instanceof Float32Array ) 
  { (new Float32Array(buffer.getMappedRange())).set(arrData) }
  else 
  { (new Uint16Array (buffer.getMappedRange())).set(arrData) }
  buffer.unmap();
  return buffer;
}

// Declare buffer handles (GPUBuffer)
var positionBuffer = createBuffer(positions, GPUBufferUsage.VERTEX);
var colorBuffer    = createBuffer(colors,    GPUBufferUsage.VERTEX);
var indexBuffer    = createBuffer(indices,   GPUBufferUsage.INDEX);

const pipeline = device.createRenderPipeline({
  layout: 'auto',
  vertex:    { module     : device.createShaderModule({code   : vertWGSL }),
               entryPoint : 'main',
               buffers    : [ { arrayStride: 12, attributes: [{ shaderLocation: 0,
                                                                format: "float32x3",
                                                                offset: 0  }]         },
                              { arrayStride: 12, attributes: [{ shaderLocation: 1,
                                                                format: "float32x3",
                                                                offset: 0  }]         }
    ]
  },
  fragment:  { module     : device.createShaderModule({ code  : fragWGSL }),
               entryPoint : 'main',
               targets    : [ {format: presentationFormat } ],
  },
  primitive: {
    topology: "triangle-list",
    cullMode: 'back'
  },
  multisample: {
    count: sampleCount,
  },
});


var resolveTarget = undefined;
var view          = undefined;
if ( sampleCount > 1 )
{
  const outtexture = device.createTexture({
    size: [canvas.width, canvas.height],
    sampleCount: sampleCount,
    format: presentationFormat,
    usage: GPUTextureUsage.RENDER_ATTACHMENT,
  });
  view          = outtexture.createView();
  resolveTarget = context.getCurrentTexture().createView();
}
else
{
  view =  context.getCurrentTexture().createView();
}

function frame() 
{
  const renderPassDescription = {
  colorAttachments: [{
      view : view,
      resolveTarget: resolveTarget,
      loadOp:"clear", clearValue: [0, 0.5, 0.5, 1], // clear screen to color
      storeOp: 'store'
    }],
  };
  
  //renderPassDescription.colorAttachments[0].view = outview; // context.getCurrentTexture().createView();
  
  const commandEncoder = device.createCommandEncoder();
  const renderPass = commandEncoder.beginRenderPass(renderPassDescription);

  renderPass.setPipeline(pipeline);
  renderPass.setVertexBuffer(0, positionBuffer);
  renderPass.setVertexBuffer(1, colorBuffer);
  renderPass.setIndexBuffer(indexBuffer, 'uint16');
  renderPass.drawIndexed(3,1);
  renderPass.end();

  device.queue.submit([commandEncoder.finish()]);
} 

frame();

// only update when moving the mouse (modified to update all time)
onmousemove = function() {
  frame();
}

console.log('ready...');