{"topic":{"id":13805,"title":"2.8 局部操作无法选中点线面","slug":"topic","categoryId":56,"createdAt":"2024-11-04 13:29:54.229872","bumpedAt":"2024-11-07 08:17:44.040091","views":222,"postsCount":5,"highestPostNumber":5,"likeCount":2,"closed":false,"pinned":false,"pinnedGlobally":false,"pinnedAt":null,"pinnedUntil":null,"isBanner":false,"excerpt":"文档中说启动 Dandelion，加载 cube.obj 并进入建模模式 (model mode) 就可以看到用箭头表示的半边。直接点击某条半边就可以选中它，此时点击 Local Operations 一栏下的 Inverse, Next, Previous 等按钮就可以在这条半边连接的元素之间切换（如图 1.5 右侧所示）。但是我无法选中","deletedAt":null,"isAnonymous":false,"category":{"id":56,"name":"计算机图形学","slug":"cg","color":"92278F"},"author":{"id":279,"username":"xiu","name":"xiu","avatarUrl":"/uploads/image/0a/1a/0a1a239b4961fe98a2b1f6db28b7fc9c394f6c7c0a0b73b924cadb1019cb656d.avif"},"tags":[]},"posts":[{"id":42624,"postNumber":1,"raw":"![屏幕快照 2024-11-04 的 21.26.46 下午|630x500](/uploads/image/bc/b8/bcb87718a5fd8a753c573f24ce26eb6bd1e4f98d8ba52c5f1b9a66d4edbd16ed.avif)\n\n文档中说\n> 启动 Dandelion，加载 cube.obj 并进入建模模式 (model mode) 就可以看到用箭头表示的半边。直接点击某条半边就可以选中它，此时点击 Local Operations 一栏下的 Inverse, Next, Previous 等按钮就可以在这条半边连接的元素之间切换（如图 1.5 右侧所示）。\n\n但是我无法选中","cooked":"

$\"屏幕快照$

文档中说

\n
启动 Dandelion，加载 cube.obj 并进入建模模式 (model mode) 就可以看到用箭头表示的半边。直接点击某条半边就可以选中它，此时点击 Local Operations 一栏下的 Inverse, Next, Previous 等按钮就可以在这条半边连接的元素之间切换（如图 1.5 右侧所示）。
\n

但是我无法选中

\n","createdAt":"2024-11-04 13:29:54.434637","updatedAt":"2024-11-04 13:51:57.891839","replyToPostNumber":null,"replyCount":0,"likeCount":0,"wordCount":109,"liked":false,"bookmarked":false,"polls":[],"reactions":[],"wiki":false,"version":2,"publicVersion":2,"deletedAt":null,"isAnonymous":false,"user":{"id":279,"username":"xiu","name":"xiu","avatarUrl":"/uploads/image/0a/1a/0a1a239b4961fe98a2b1f6db28b7fc9c394f6c7c0a0b73b924cadb1019cb656d.avif","admin":false,"moderator":false,"signatureRaw":null,"signatureCooked":null}},{"id":42630,"postNumber":2,"raw":"请问各位大佬有没有遇到类似的问题？\n或者正确的操作方式是什么？","cooked":"

请问各位大佬有没有遇到类似的问题？
\n或者正确的操作方式是什么？

\n","createdAt":"2024-11-04 14:02:16.432312","updatedAt":"2024-11-04 14:02:16.432312","replyToPostNumber":null,"replyCount":0,"likeCount":0,"wordCount":30,"liked":false,"bookmarked":false,"polls":[],"reactions":[],"wiki":false,"version":1,"publicVersion":1,"deletedAt":null,"isAnonymous":false,"user":{"id":279,"username":"xiu","name":"xiu","avatarUrl":"/uploads/image/0a/1a/0a1a239b4961fe98a2b1f6db28b7fc9c394f6c7c0a0b73b924cadb1019cb656d.avif","admin":false,"moderator":false,"signatureRaw":null,"signatureCooked":null}},{"id":42672,"postNumber":3,"raw":"![截屏 2024-11-06 00.10.49|690x445](/uploads/image/7c/a5/7ca50c7bd5d905caef9efcd22c5709eaa6622cc8845e8b2e879f5b74995911e5.avif)\n如图只能选中物体","cooked":"

$\"截屏$
\n如图只能选中物体

\n","createdAt":"2024-11-05 16:11:47.73565","updatedAt":"2024-11-05 16:11:47.73565","replyToPostNumber":null,"replyCount":0,"likeCount":0,"wordCount":13,"liked":false,"bookmarked":false,"polls":[],"reactions":[],"wiki":false,"version":1,"publicVersion":1,"deletedAt":null,"isAnonymous":false,"user":{"id":279,"username":"xiu","name":"xiu","avatarUrl":"/uploads/image/0a/1a/0a1a239b4961fe98a2b1f6db28b7fc9c394f6c7c0a0b73b924cadb1019cb656d.avif","admin":false,"moderator":false,"signatureRaw":null,"signatureCooked":null}},{"id":42830,"postNumber":4,"raw":"我试着分析一下：\n\n1. 首先你能选中物体，也能正常进入建模模式，那运行时兼容性出问题的可能性比较小，姑且先假定没有问题。\n2. 日志里可以看到若干 `perform picking` 记录，说明射线打出去了，求交过程是存在的，但没求到交点。\n\ndandelion 的拾取功能是基于射线求交的，而射线又是根据投影矩阵构造的。在实现正确的透视投影矩阵之前，打出去的射线位置与屏幕上点击的位置会有不小的偏差，所以求交很容易出错。而具体的偏差值与窗口大小和视角位置有关，所以特定的屏幕上选不中是有可能出现的问题。\n\n我建议这样试一遍：\n\n1. 从 GitHub 上下载预编译版本，看看预编译版本能不能正常拾取。如果能，继续往下试；\n2. 打开菜单栏上的 *Debug > Debug Options > Show Picking Ray* 选项，让 dandelion 绘制点击时构造的拾取射线。此时再尝试点选模型，观察 picking ray。如果点击后看不到射线，稍微旋转视角后看到射线打中了你点击的位置，那么请联系我们当面调试；如果点击后就能看到射线，且射线明显打偏了，那么你需要先实现好透视投影矩阵 (`Camera::projection`) 。","cooked":"

我试着分析一下：

首先你能选中物体，也能正常进入建模模式，那运行时兼容性出问题的可能性比较小，姑且先假定没有问题。
日志里可以看到若干 perform picking 记录，说明射线打出去了，求交过程是存在的，但没求到交点。

dandelion 的拾取功能是基于射线求交的，而射线又是根据投影矩阵构造的。在实现正确的透视投影矩阵之前，打出去的射线位置与屏幕上点击的位置会有不小的偏差，所以求交很容易出错。而具体的偏差值与窗口大小和视角位置有关，所以特定的屏幕上选不中是有可能出现的问题。

我建议这样试一遍：

从 GitHub 上下载预编译版本，看看预编译版本能不能正常拾取。如果能，继续往下试；
打开菜单栏上的 Debug > Debug Options > Show Picking Ray 选项，让 dandelion 绘制点击时构造的拾取射线。此时再尝试点选模型，观察 picking ray。如果点击后看不到射线，稍微旋转视角后看到射线打中了你点击的位置，那么请联系我们当面调试；如果点击后就能看到射线，且射线明显打偏了，那么你需要先实现好透视投影矩阵 (Camera::projection) 。

\n","createdAt":"2024-11-07 05:02:39.451677","updatedAt":"2024-11-07 05:02:39.451677","replyToPostNumber":null,"replyCount":1,"likeCount":1,"wordCount":394,"liked":false,"bookmarked":false,"polls":[],"reactions":[{"reaction":"❤️","count":1,"users":[{"id":4668,"username":"IO","name":null}],"hasReacted":false}],"wiki":false,"version":1,"publicVersion":1,"deletedAt":null,"isAnonymous":false,"user":{"id":1381,"username":"greyishsong","name":"greyishsong","avatarUrl":"/uploads/image/da/bc/dabc731b0311f59850625bbeb55ed969fcfac0430c5ef0f68441e5466b7aa496.avif","admin":false,"moderator":true,"signatureRaw":null,"signatureCooked":null}},{"id":42831,"postNumber":5,"raw":"而且不难发现如果改了 CMakeLists.txt 里的`#debug dandelion-ray-debug #optimized dandelion-ray`链接库，并且在 utils/ray.cpp 里的 `generate_ray` 函数在实验中没有正确实现，也会影响结果。","cooked":"

而且不难发现如果改了 CMakeLists.txt 里的#debug dandelion-ray-debug #optimized dandelion-ray链接库，并且在 utils/ray.cpp 里的 generate_ray 函数在实验中没有正确实现，也会影响结果。

\n","createdAt":"2024-11-07 08:17:44.040091","updatedAt":"2024-11-07 08:17:44.040091","replyToPostNumber":4,"replyCount":0,"likeCount":1,"wordCount":48,"liked":false,"bookmarked":false,"polls":[],"reactions":[{"reaction":"❤️","count":1,"users":[{"id":1381,"username":"greyishsong","name":"greyishsong"}],"hasReacted":false}],"wiki":false,"version":1,"publicVersion":1,"deletedAt":null,"isAnonymous":false,"user":{"id":3740,"username":"Lskyi","name":null,"avatarUrl":null,"admin":false,"moderator":false,"signatureRaw":null,"signatureCooked":null}}],"hasMore":false,"lastReadPostNumber":5,"hasUrlPostNumber":true}