Add bilinear interpolation for texture maps

scenes/earth.json

@@ -51,7 +51,8 @@
  "spherical": {
  "uv-pattern": {
  "image": {
- "file": "earthmap1k.png"
+ "file": "earthmap1k.png",
+ "interpolation": "bilinear"
  }
  }
  }

src/parsing/scene.zig

@@ -70,6 +70,7 @@ fn UvPatternConfig(comptime T: type) type {
  },
  image: struct {
  file: []const u8,
+ interpolation: enum { none, bilinear } = .none,
  },
  };
 }
@@ -282,7 +283,13 @@ fn parseUvPattern(
  defer im.deinit();
 
  const canvas = try Canvas(T).fromImage(arena_allocator, im);
- break :blk UvPattern(T).uvImage(canvas);
+ break :blk UvPattern(T).uvImage(
+ canvas,
+ switch (image.interpolation) {
+ .none => .None,
+ .bilinear => .Bilinear
+ }
+ );
  },
  }
  };

src/raytracer/patterns/texture_map.zig

@@ -65,8 +65,10 @@ fn UvCheckers(comptime T: type) type {
 fn UvImage(comptime T: type) type {
  return struct {
  const Self = @This();
+ const Interpolation = enum { None, Bilinear };
 
  canvas: Canvas(T),
+ interpolation: Interpolation,
 
  fn uvPatternAt(self: Self, u: T, v: T, object_point: Tuple(T)) Color(T) {
  _ = object_point;
@@ -76,7 +78,28 @@ fn UvImage(comptime T: type) type {
  const x = u * @as(T, @floatFromInt(self.canvas.width - 1));
  const y = v_flip * @as(T, @floatFromInt(self.canvas.height - 1));
 
- return self.canvas.getPixelPointer(@intFromFloat(@round(x)), @intFromFloat(@round(y))).?.*;
+ switch (self.interpolation) {
+ .None => {
+ return self.canvas.getPixelPointer(@intFromFloat(@round(x)), @intFromFloat(@round(y))).?.*;
+ },
+ .Bilinear => {
+ const x1 = @floor(x);
+ const x2 = @ceil(x);
+ const y1 = @floor(y);
+ const y2 = @ceil(y);
+
+ const color_11 = self.canvas.getPixelPointer(@intFromFloat(x1), @intFromFloat(y1)).?.*;
+ const color_21 = self.canvas.getPixelPointer(@intFromFloat(x2), @intFromFloat(y1)).?.*;
+ const color_12 = self.canvas.getPixelPointer(@intFromFloat(x1), @intFromFloat(y2)).?.*;
+ const color_22 = self.canvas.getPixelPointer(@intFromFloat(x2), @intFromFloat(y2)).?.*;
+
+ const color_x1 = color_11.mul(x2 - x).add(color_21.mul(x - x1));
+ const color_x2 = color_12.mul(x2 - x).add(color_22.mul(x - x1));
+
+ const color_xy = color_x1.mul(y2 - y).add(color_x2.mul(y - y1));
+ return color_xy;
+ }
+ }
  }
  };
 }
@@ -124,8 +147,8 @@ pub fn UvPattern(comptime T: type) type {
  };
  }
 
- pub fn uvImage(canvas: Canvas(T)) Self {
- return .{ .variant = .{ .uv_image = .{ .canvas = canvas } } };
+ pub fn uvImage(canvas: Canvas(T), interpolation: UvImage(T).Interpolation) Self {
+ return .{ .variant = .{ .uv_image = .{ .canvas = canvas, .interpolation = interpolation } } };
  }
 
  fn uvPatternAt(self: Self, u: T, v: T, object_point: Tuple(T)) Color(T) {
@@ -536,7 +559,7 @@ test "Canvas-based checker pattern in 2D" {
  const canvas = try Canvas(f32).fromPpm(allocator, ppm);
  defer canvas.destroy();
 
- const uv_pattern = UvPattern(f32).uvImage(canvas);
+ const uv_pattern = UvPattern(f32).uvImage(canvas, .None);
 
  try testing.expect(uv_pattern.uvPatternAt(0.0, 0.0, undefined).approxEqual(Color(f32).new(0.9, 0.9, 0.9)));
  try testing.expect(uv_pattern.uvPatternAt(0.3, 0.0, undefined).approxEqual(Color(f32).new(0.2, 0.2, 0.2)));