C# 呼叫 Google Earth COM API 開發（四）：滑鼠滾輪縮放實作

利用滑鼠鉤子攔截滾輪事件，向 Google Earth 渲染視窗發送 WM_MOUSEWHEEL 訊息實現放大/縮小。

滾輪事件處理

private const long ZoomIn = 0x00780000;
private const long ZoomOut = 0xFF880000;

mouseHook.MouseWheel += mouseHook_MouseWheel;

void mouseHook_MouseWheel(object sender, MouseEventArgs e) {
    IntPtr hWnd = NativeMethods.WindowFromPoint(e.Location);
    if (hWnd == this.GeRenderHWnd) {
        Point pt = this.Control.PointToClient(e.Location);
        if (this.Control.ClientRectangle.Contains(pt)) {
            NativeMethods.PostMessage(GeRenderHWnd, (int)WM_MOUSE.WM_MOUSEWHEEL,
                e.Delta == 120 ? ZoomIn : ZoomOut, 0);
        }
    }
}

e.Delta 正值為向前滾動（放大），負值為向後（縮小）。此法解決了第三篇僅能放大的限制。