feat(文件拆分): 拆分几何三维基础能力

internal/base/threed/u3d_view_bounds.go

@@ -0,0 +1,39 @@
+// Copyright 2025-2026 肖其顿 (XIAO QI DUN)
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package threed
+
+import (
+	"image"
+	"math"
+)
+
+// viewImageBounds 计算采样器可能写入的像素范围，并在整数转换前裁至目标边界
+// 入参: source 原始像素边界, m 像素变换, target 目标边界
+// 返回: image.Rectangle 受影响的目标像素区域
+func viewImageBounds(source image.Rectangle, m [6]float64, target image.Rectangle) image.Rectangle {
+	minX, minY, maxX, maxY := math.Inf(1), math.Inf(1), math.Inf(-1), math.Inf(-1)
+	for _, p := range [4]image.Point{source.Min, {X: source.Max.X, Y: source.Min.Y}, {X: source.Min.X, Y: source.Max.Y}, source.Max} {
+		x := math.Floor(float64(m[0]*float64(p.X)) + float64(m[2]*float64(p.Y)) + m[4])
+		y := math.Floor(float64(m[1]*float64(p.X)) + float64(m[3]*float64(p.Y)) + m[5])
+		minX, minY = math.Min(minX, x), math.Min(minY, y)
+		maxX, maxY = math.Max(maxX, x+1), math.Max(maxY, y+1)
+	}
+	minX, minY = math.Max(minX, float64(target.Min.X)), math.Max(minY, float64(target.Min.Y))
+	maxX, maxY = math.Min(maxX, float64(target.Max.X)), math.Min(maxY, float64(target.Max.Y))
+	if minX >= maxX || minY >= maxY {
+		return image.Rectangle{}
+	}
+	return image.Rect(int(minX), int(minY), int(maxX), int(maxY))
+}