src/webgpu/multisample_info.ts

/* Data used for multisample tests */

const samplePositionToFragmentPosition = (pos: readonly number[]): readonly number[] =>
  pos.map(v => v / 16);
const samplePositionsToFragmentPositions = (
  positions: readonly (readonly number[])[]
): readonly (readonly number[])[] => positions.map(samplePositionToFragmentPosition);

// These are sample positions based on a 16x16 grid with 0,0 at the top left.
// For example 8,8 would be a fragment coordinate of 0.5, 0.5
// Based on: https://learn.microsoft.com/en-us/windows/win32/api/d3d11/ne-d3d11-d3d11_standard_multisample_quality_levels
const kMultisamplingTables = new Map<number, readonly (readonly number[])[]>([
  [1, samplePositionsToFragmentPositions([[8, 8]])],
  [
    2,
    samplePositionsToFragmentPositions([
      [4, 4],
      [12, 12],
    ]),
  ],
  [
    4,
    samplePositionsToFragmentPositions([
      [6, 2],
      [14, 6],
      [2, 10],
      [10, 14],
    ]),
  ],
  [
    8,
    samplePositionsToFragmentPositions([
      [9, 5],
      [7, 11],
      [13, 9],
      [5, 3],
      [3, 13],
      [1, 7],
      [11, 15],
      [15, 1],
    ]),
  ],
  [
    16,
    samplePositionsToFragmentPositions([
      [9, 9],
      [7, 5],
      [5, 10],
      [12, 7],

      [3, 6],
      [10, 13],
      [13, 11],
      [11, 3],

      [6, 14],
      [8, 1],
      [4, 2],
      [2, 12],

      [0, 8],
      [15, 4],
      [14, 15],
      [1, 0],
    ]),
  ],
]);

/**
 * For a given sampleCount returns an array of 2d fragment offsets
 * where each offset is between 0 and 1.
 */
export function getMultisampleFragmentOffsets(sampleCount: number) {
  return kMultisamplingTables.get(sampleCount)!;
}