{"topic":{"id":13867,"title":"实验 2.2 视口坐标下的.w() 和世界坐标下的.z() 的选取不同深度矫正插值产生影响","slug":"topic","categoryId":56,"createdAt":"2024-11-15 09:11:38.442563","bumpedAt":"2024-11-17 07:07:45.046604","views":176,"postsCount":2,"highestPostNumber":2,"likeCount":0,"closed":false,"pinned":false,"pinnedGlobally":false,"pinnedAt":null,"pinnedUntil":null,"isBanner":false,"excerpt":"文档中说透视投影后的 w 表示的是透视投影前的 z 值。所以我试了试，使用透视投影前的.z() 值时： Vector3f Zt = {t.world_pos[0].z(), t.world_pos[1].z(), t.world_pos[2].z()}; 得到的图片是这样的：图中用红线圈起来的地方可以看到黑点，尤其是奶牛腰部的地方失真还挺严重的。使用透视投影后的.w() 值时： Vector3f Zt = {t.viewport…","deletedAt":null,"isAnonymous":false,"category":{"id":56,"name":"计算机图形学","slug":"cg","color":"92278F"},"author":{"id":259,"username":"ReturnDream","name":"保密","avatarUrl":null},"tags":[]},"posts":[{"id":43300,"postNumber":1,"raw":"\n文档中说\n\n> 透视投影后的 w 表示的是透视投影前的 z 值。\n\n所以我试了试，使用透视投影前的.z() 值时：\n```\nVector3f Zt = {t.world_pos[0].z(), t.world_pos[1].z(), t.world_pos[2].z()};\n```\n得到的图片是这样的：\n![ver2__(1)|480x360](/uploads/image/cd/af/cdaf7e62c82d7cf14824a19164bca0074f89b14321440e19cb12ae42ff3e6d36.avif)\n图中用红线圈起来的地方可以看到黑点，尤其是奶牛腰部的地方失真还挺严重的。\n\n使用透视投影后的.w() 值时：\n```\nVector3f Zt = {t.viewport_pos[0].w(), t.viewport_pos[1].w(), t.viewport_pos[2].w()};\n```\n渲染出来的奶牛就正常了：\n![ver1__|480x360](/uploads/image/5d/14/5d14f9f77fc98102c87fbcd2b1d98a5f3368be5b4aa1781bca8f423353eb3bd2.avif)\n\n这样看来透视投影后的.w() 跟透视投影前的.z() 应该有点区别啊？\n\n(ps：\n写着写着这个帖子自己想明白了:joy:。透视投影后的.w() 跟透视投影前的.z() 确有相反数的关系，但是我在顶点渲染器里对 world_pos 和 viewport_pos 进行实际计算的方法不一样，所以它俩计算出来的值应该有细微的差别，这种细微的差别导致了第一张图的黑点。\n不过不太确定黑点的具体成因，按理说是片元/像素的 color 值为 0 了，但是根据着色器的计算，片元不太可能真黑，应该是深度检测出了问题吧，导致后面的黑色块被判定成在前面了。 \n\n**另外，**\n```\n // set Uniforms for vertex shader\n Uniforms::MVP = cam.projection() * cam.view() * object->model();\n Uniforms::inv_trans_M = object->model().inverse().transpose();\n Uniforms::width = static_cast(this->width);\n Uniforms::height = static_cast(this->height);\n // To do: 同步\n Uniforms::material = object->mesh.material;\n Uniforms::lights = scene.lights;\n Uniforms::camera = scene.camera;\n```\n这部分代码我未做任何改动仍然能渲染出 2.2 所要求的结果。此处的 To do 是否是不必要的？","cooked":"

文档中说

\n
透视投影后的 w 表示的是透视投影前的 z 值。
\n

所以我试了试，使用透视投影前的.z() 值时：

Vector3f Zt = {t.world_pos[0].z(), t.world_pos[1].z(), t.world_pos[2].z()};\n

得到的图片是这样的：
\n $\"ver2__(1)\"$
\n图中用红线圈起来的地方可以看到黑点，尤其是奶牛腰部的地方失真还挺严重的。

使用透视投影后的.w() 值时：

Vector3f Zt = {t.viewport_pos[0].w(), t.viewport_pos[1].w(), t.viewport_pos[2].w()};\n

渲染出来的奶牛就正常了：
\n $\"ver1__\"$

这样看来透视投影后的.w() 跟透视投影前的.z() 应该有点区别啊？

(ps：
\n写着写着这个帖子自己想明白了😂。透视投影后的.w() 跟透视投影前的.z() 确有相反数的关系，但是我在顶点渲染器里对 world_pos 和 viewport_pos 进行实际计算的方法不一样，所以它俩计算出来的值应该有细微的差别，这种细微的差别导致了第一张图的黑点。
\n不过不太确定黑点的具体成因，按理说是片元/像素的 color 值为 0 了，但是根据着色器的计算，片元不太可能真黑，应该是深度检测出了问题吧，导致后面的黑色块被判定成在前面了。

另外，

            // set Uniforms for vertex shader\n            Uniforms::MVP         = cam.projection() * cam.view() * object->model();\n            Uniforms::inv_trans_M = object->model().inverse().transpose();\n            Uniforms::width       = static_cast<int>(this->width);\n            Uniforms::height      = static_cast<int>(this->height);\n            // To do: 同步\n            Uniforms::material = object->mesh.material;\n            Uniforms::lights   = scene.lights;\n            Uniforms::camera   = scene.camera;\n

这部分代码我未做任何改动仍然能渲染出 2.2 所要求的结果。此处的 To do 是否是不必要的？

\n","createdAt":"2024-11-15 09:11:38.761161","updatedAt":"2024-11-15 09:11:38.761161","replyToPostNumber":null,"replyCount":0,"likeCount":0,"wordCount":424,"liked":false,"bookmarked":false,"polls":[],"reactions":[],"wiki":false,"version":1,"publicVersion":1,"deletedAt":null,"isAnonymous":false,"user":{"id":259,"username":"ReturnDream","name":"保密","avatarUrl":null,"admin":false,"moderator":false,"signatureRaw":null,"signatureCooked":null}},{"id":43327,"postNumber":2,"raw":"只做 2.2 的话可以不用考虑","cooked":"

只做 2.2 的话可以不用考虑

\n","createdAt":"2024-11-17 07:07:45.046604","updatedAt":"2024-11-17 07:07:45.046604","replyToPostNumber":null,"replyCount":0,"likeCount":0,"wordCount":11,"liked":false,"bookmarked":false,"polls":[],"reactions":[],"wiki":false,"version":1,"publicVersion":1,"deletedAt":null,"isAnonymous":false,"user":{"id":1484,"username":"storm314","name":null,"avatarUrl":"/uploads/image/82/4a/824ae9f755bc5939263c9836cf3262719c5e957f5f685b959d66efd39b5bcc59.avif","admin":false,"moderator":false,"signatureRaw":null,"signatureCooked":null}}],"hasMore":false,"lastReadPostNumber":1,"hasUrlPostNumber":false}