使用 Stencil-buffer 绘制 3D 模型的轮廓
Outlining a 3D model using Stencil-buffer
首先，我想提一下，我发现我认为是完全相同的问题，不幸的是没有答案，在这里：
Java Using OpenGL Stencil to create Outline
我将 post 我的代码放在下面，但首先是问题：从这个捕获**，您可以看到显示了整个框架结构，而不是围绕球体的单条线。我想摆脱里面的所有那些线！
** 显然我不能添加图片：看这个 link - 想象一个球体，其四边形的所有边缘都以 3 像素大线可见。
http://srbwks36224-03.engin.umich.edu/kdi/images/gs_sphere_with_frame.jpg
这是给出该结果的代码：
// First render the sphere:
// inside "show" is all the code to display a textured sphere
// looking like earth
sphe->show();
// Now get ready for stencil buffer drawing pass:
// 1. Clear and initialize it
// 2. Activate stencil buffer
// 3. On the first rendering pass, we want to "SUCCEED ALWAYS"
// and write a "1" into the stencil buffer accordingly
// 4. We don't need to actually render the object, hence disabling RGB mask
glClearStencil(0); //Edit: swapped this line and below
glClear(GL_STENCIL_BUFFER_BIT);
glEnable(GL_STENCIL_TEST);
glStencilFunc(GL_NEVER, 0x1, 0x1); //Edit: GL_ALWAYS
glStencilOp(GL_REPLACE, GL_KEEP, GL_KEEP); //Edit: GL_KEEP, GL_KEEP, GL_REPLACE
glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);
glDepthMask(GL_FALSE); // As per Andon's comment
sphe->show();
// At this point, I expect to have "1" on the entire
// area covered by the sphere, so...
// 1. Stencil test should fail for anything, but 0 value
// RM: commented is another option that should work too I believe
// 2. The stencil op instruction at the point is somewhat irrelevant
// (if my understanding is correct), because we won't do anything
// else with the stencil buffer after that.
// 3. Re-enable RGB mask, because we want to draw this time
// 4. Switch to LINE drawing instead of FILL and
// 5. set a bigger line width, so it will exceed the model boundaries.
// We do want this, otherwise the line would not show
// 6. Don't mind the "uniform" setting instruction, this is so
// that my shader knows it should draw in plain color
// 7. Draw the sphere's frame
// 8. The principle, as I understand it is that all the lines should
// find themselves matched to a "1" in the stencil buffer and therefore
// be ignored for rendering. Only lines on the edges of the model should
// have half their width not failing the stencil test.
glStencilFunc(GL_EQUAL, 0x0, 0x1);
//glStencilFunc(GL_NOTEQUAL, 0x1, 0x1);
glStencilOp(GL_KEEP, GL_KEEP, GL_REPLACE);
glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
glDepthMask(GL_TRUE);
glLineWidth(3);
glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
psa::shader::setUniform("outlining", 1);
sphe->show();
psa::shader::setUniform("outlining", 0);
现在只是为了证明一点，我厌倦了使用模板缓冲区做一些不同的事情 - 我只是想确保我的代码中的一切都已到位，以使其正常工作。
** 再次不幸的是，我无法显示我得到的结果的屏幕截图：场景是这样的
http://mathworld.wolfram.com/images/eps-gif/SphereSphereInterGraphic_700.gif
但是较小的球体是不可见的（RGB 遮罩已停用）并且可以通过孔看到世界背景（而不是较大球体的内部 - 面部剔除已停用）。
这是代码...有趣的是，我可以更改很多东西，例如 activate/deactivate 和 STENCIL_TEST，将操作更改为 GL_KEEP，甚至将第二个 stencilFunc 更改为 "NOT EQUAL 0"...结果总是一样的！我想我在这里遗漏了一些基本的东西。
void testStencil()
{
// 1. Write a 1 in the Stencil buffer for
// every pixels of the first sphere:
// All colors disabled, we don't need to see that sphere
glEnable(GL_STENCIL_TEST);
glStencilFunc(GL_ALWAYS, 0x1, 0x1);
glStencilOp(GL_KEEP, GL_KEEP, GL_REPLACE);
glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);
glDepthMask(GL_FALSE); // Edit: added this
{
sphe->W = mat4::trans(psa::vec4(1.0, 1.0, 1.0)) * mat4::scale(0.9);
sphe->show();
}
// 2. Draw the second sphere with the following rule:
// fail the stencil test for every pixels with a 1.
// This means that any pixel from first sphere will
// not be draw as part of the second sphere.
glStencilFunc(GL_EQUAL, 0x0, 0x1);
glStencilOp(GL_KEEP, GL_KEEP, GL_REPLACE);
glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
glDepthMask(GL_TRUE); // Edit: added this
{
sphe->W = mat4::trans(psa::vec4(1.2, 1.2, 1.2)) * mat4::scale(1.1);
sphe->show();
}
}
瞧瞧！如果有人能指出我正确的方向，我将不胜感激。我也会确保将你的答案参考我发现的另一个 post。
这个问题中的 OpenGL 代码 post 有效。问题的原因在于windowinitialization/creation：
下面分别是有效代码的 SDL1.2 和 SDL2 版本。请注意，在这两种情况下，SetAttribute 语句都放在 window 创建之前。主要问题是错放的语句不一定会在 运行 时失败，但也不会起作用。
SDL1.2:
if(SDL_Init(SDL_INIT_EVERYTHING) < 0)
{
throw "Video initialization failed";
}
SDL_GL_SetAttribute(SDL_GL_RED_SIZE, 5);
SDL_GL_SetAttribute(SDL_GL_GREEN_SIZE, 5);
SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE, 5);
SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24);
SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE, 8);
SDL_GL_SetAttribute(SDL_GL_MULTISAMPLEBUFFERS, 1);
SDL_GL_SetAttribute(SDL_GL_MULTISAMPLESAMPLES,16);
SDL_GL_SetAttribute(SDL_GL_ACCELERATED_VISUAL, 1);
const SDL_VideoInfo * i;
if((i = SDL_GetVideoInfo()) == NULL)
{
throw "Video query failed";
}
int flag = (fs ? SDL_OPENGL | SDL_FULLSCREEN : SDL_OPENGL);
if(SDL_SetVideoMode(w, h, i->vfmt->BitsPerPixel, flag) == 0)
{
throw "Video mode set failed";
}
glewExperimental = GL_TRUE;
if(glewInit() != GLEW_OK)
{
throw "Could not initialize GLEW";
}
if(!glewIsSupported("GL_VERSION_3_3"))
{
throw "OpenGL 3.3 not supported";
}
SDL2（本质上是相同的代码，只是 window 创建函数发生了变化）：
if(SDL_Init(SDL_INIT_EVERYTHING) < 0)
{
throw "Video initialization failed";
}
SDL_GL_SetAttribute(SDL_GL_RED_SIZE, 5);
SDL_GL_SetAttribute(SDL_GL_GREEN_SIZE, 5);
SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE, 5);
SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24);
SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE, 8);
SDL_GL_SetAttribute(SDL_GL_MULTISAMPLEBUFFERS, 1);
SDL_GL_SetAttribute(SDL_GL_MULTISAMPLESAMPLES,16);
SDL_GL_SetAttribute(SDL_GL_ACCELERATED_VISUAL, 1);
int flag = SDL_WINDOW_OPENGL;
if((win = SDL_CreateWindow("engine", 100, 100, w, h, flag)) == NULL)
{
throw "Create SDL Window failed";
}
context = SDL_GL_CreateContext(win);
glewExperimental = GL_TRUE;
if(glewInit() != GLEW_OK)
{
throw "Could not initialize GLEW";
}
if(!glewIsSupported("GL_VERSION_3_3"))
{
throw "OpenGL 3.3 not supported";
}
有几点值得一提：
1。尽管我知道不建议这样做，但 SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE, 1) 也可以
2。在 SDL2 中，SDL_GL_SetAttribute SDL_GL_MULTISAMPLESAMPLES 对我来说上升到 16，在 glewInit() 失败之后，但是，在 window 创建之后移动多重采样设置，然后 glewInit 突然停止抱怨：我的猜测是它只是被忽略了。
3。在 SDL1.2 中，Multisampling "seem" 的任何值都可以工作
4。考虑到模板缓冲区功能，只有下面的代码也可以工作，但我 post 它本质上是为了提出一个问题：有多少属性设置在实际工作？以及如何知道，因为代码编译并且 运行s 没有明显的问题？
// PROBABLY WRONG:
// ----
SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE, 8);
const SDL_VideoInfo * i;
if((i = SDL_GetVideoInfo()) == NULL)
{
throw "Video query failed";
}
int flag = (fs ? SDL_OPENGL | SDL_FULLSCREEN : SDL_OPENGL);
if(SDL_SetVideoMode(w, h, i->vfmt->BitsPerPixel, flag) == 0)
{
throw "Video mode set failed";
}
// No idea if the below is actually applied!
SDL_GL_SetAttribute(SDL_GL_RED_SIZE, 5);
SDL_GL_SetAttribute(SDL_GL_GREEN_SIZE, 5);
SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE, 5);
SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24);
SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
SDL_GL_SetAttribute(SDL_GL_MULTISAMPLEBUFFERS, 1);
SDL_GL_SetAttribute(SDL_GL_MULTISAMPLESAMPLES, 16);
SDL_GL_SetAttribute(SDL_GL_ACCELERATED_VISUAL, 1);
首先，我想提一下，我发现我认为是完全相同的问题，不幸的是没有答案，在这里： Java Using OpenGL Stencil to create Outline
我将 post 我的代码放在下面，但首先是问题：从这个捕获**，您可以看到显示了整个框架结构，而不是围绕球体的单条线。我想摆脱里面的所有那些线！
** 显然我不能添加图片：看这个 link - 想象一个球体，其四边形的所有边缘都以 3 像素大线可见。
http://srbwks36224-03.engin.umich.edu/kdi/images/gs_sphere_with_frame.jpg
这是给出该结果的代码：
// First render the sphere:
// inside "show" is all the code to display a textured sphere
// looking like earth
sphe->show();
// Now get ready for stencil buffer drawing pass:
// 1. Clear and initialize it
// 2. Activate stencil buffer
// 3. On the first rendering pass, we want to "SUCCEED ALWAYS"
// and write a "1" into the stencil buffer accordingly
// 4. We don't need to actually render the object, hence disabling RGB mask
glClearStencil(0); //Edit: swapped this line and below
glClear(GL_STENCIL_BUFFER_BIT);
glEnable(GL_STENCIL_TEST);
glStencilFunc(GL_NEVER, 0x1, 0x1); //Edit: GL_ALWAYS
glStencilOp(GL_REPLACE, GL_KEEP, GL_KEEP); //Edit: GL_KEEP, GL_KEEP, GL_REPLACE
glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);
glDepthMask(GL_FALSE); // As per Andon's comment
sphe->show();
// At this point, I expect to have "1" on the entire
// area covered by the sphere, so...
// 1. Stencil test should fail for anything, but 0 value
// RM: commented is another option that should work too I believe
// 2. The stencil op instruction at the point is somewhat irrelevant
// (if my understanding is correct), because we won't do anything
// else with the stencil buffer after that.
// 3. Re-enable RGB mask, because we want to draw this time
// 4. Switch to LINE drawing instead of FILL and
// 5. set a bigger line width, so it will exceed the model boundaries.
// We do want this, otherwise the line would not show
// 6. Don't mind the "uniform" setting instruction, this is so
// that my shader knows it should draw in plain color
// 7. Draw the sphere's frame
// 8. The principle, as I understand it is that all the lines should
// find themselves matched to a "1" in the stencil buffer and therefore
// be ignored for rendering. Only lines on the edges of the model should
// have half their width not failing the stencil test.
glStencilFunc(GL_EQUAL, 0x0, 0x1);
//glStencilFunc(GL_NOTEQUAL, 0x1, 0x1);
glStencilOp(GL_KEEP, GL_KEEP, GL_REPLACE);
glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
glDepthMask(GL_TRUE);
glLineWidth(3);
glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
psa::shader::setUniform("outlining", 1);
sphe->show();
psa::shader::setUniform("outlining", 0);
现在只是为了证明一点，我厌倦了使用模板缓冲区做一些不同的事情 - 我只是想确保我的代码中的一切都已到位，以使其正常工作。
** 再次不幸的是，我无法显示我得到的结果的屏幕截图：场景是这样的
http://mathworld.wolfram.com/images/eps-gif/SphereSphereInterGraphic_700.gif
但是较小的球体是不可见的（RGB 遮罩已停用）并且可以通过孔看到世界背景（而不是较大球体的内部 - 面部剔除已停用）。
这是代码...有趣的是，我可以更改很多东西，例如 activate/deactivate 和 STENCIL_TEST，将操作更改为 GL_KEEP，甚至将第二个 stencilFunc 更改为 "NOT EQUAL 0"...结果总是一样的！我想我在这里遗漏了一些基本的东西。
void testStencil()
{
// 1. Write a 1 in the Stencil buffer for
// every pixels of the first sphere:
// All colors disabled, we don't need to see that sphere
glEnable(GL_STENCIL_TEST);
glStencilFunc(GL_ALWAYS, 0x1, 0x1);
glStencilOp(GL_KEEP, GL_KEEP, GL_REPLACE);
glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);
glDepthMask(GL_FALSE); // Edit: added this
{
sphe->W = mat4::trans(psa::vec4(1.0, 1.0, 1.0)) * mat4::scale(0.9);
sphe->show();
}
// 2. Draw the second sphere with the following rule:
// fail the stencil test for every pixels with a 1.
// This means that any pixel from first sphere will
// not be draw as part of the second sphere.
glStencilFunc(GL_EQUAL, 0x0, 0x1);
glStencilOp(GL_KEEP, GL_KEEP, GL_REPLACE);
glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
glDepthMask(GL_TRUE); // Edit: added this
{
sphe->W = mat4::trans(psa::vec4(1.2, 1.2, 1.2)) * mat4::scale(1.1);
sphe->show();
}
}
瞧瞧！如果有人能指出我正确的方向，我将不胜感激。我也会确保将你的答案参考我发现的另一个 post。
这个问题中的 OpenGL 代码 post 有效。问题的原因在于windowinitialization/creation：
下面分别是有效代码的 SDL1.2 和 SDL2 版本。请注意，在这两种情况下，SetAttribute 语句都放在 window 创建之前。主要问题是错放的语句不一定会在 运行 时失败，但也不会起作用。
SDL1.2:
if(SDL_Init(SDL_INIT_EVERYTHING) < 0)
{
throw "Video initialization failed";
}
SDL_GL_SetAttribute(SDL_GL_RED_SIZE, 5);
SDL_GL_SetAttribute(SDL_GL_GREEN_SIZE, 5);
SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE, 5);
SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24);
SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE, 8);
SDL_GL_SetAttribute(SDL_GL_MULTISAMPLEBUFFERS, 1);
SDL_GL_SetAttribute(SDL_GL_MULTISAMPLESAMPLES,16);
SDL_GL_SetAttribute(SDL_GL_ACCELERATED_VISUAL, 1);
const SDL_VideoInfo * i;
if((i = SDL_GetVideoInfo()) == NULL)
{
throw "Video query failed";
}
int flag = (fs ? SDL_OPENGL | SDL_FULLSCREEN : SDL_OPENGL);
if(SDL_SetVideoMode(w, h, i->vfmt->BitsPerPixel, flag) == 0)
{
throw "Video mode set failed";
}
glewExperimental = GL_TRUE;
if(glewInit() != GLEW_OK)
{
throw "Could not initialize GLEW";
}
if(!glewIsSupported("GL_VERSION_3_3"))
{
throw "OpenGL 3.3 not supported";
}
SDL2（本质上是相同的代码，只是 window 创建函数发生了变化）：
if(SDL_Init(SDL_INIT_EVERYTHING) < 0)
{
throw "Video initialization failed";
}
SDL_GL_SetAttribute(SDL_GL_RED_SIZE, 5);
SDL_GL_SetAttribute(SDL_GL_GREEN_SIZE, 5);
SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE, 5);
SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24);
SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE, 8);
SDL_GL_SetAttribute(SDL_GL_MULTISAMPLEBUFFERS, 1);
SDL_GL_SetAttribute(SDL_GL_MULTISAMPLESAMPLES,16);
SDL_GL_SetAttribute(SDL_GL_ACCELERATED_VISUAL, 1);
int flag = SDL_WINDOW_OPENGL;
if((win = SDL_CreateWindow("engine", 100, 100, w, h, flag)) == NULL)
{
throw "Create SDL Window failed";
}
context = SDL_GL_CreateContext(win);
glewExperimental = GL_TRUE;
if(glewInit() != GLEW_OK)
{
throw "Could not initialize GLEW";
}
if(!glewIsSupported("GL_VERSION_3_3"))
{
throw "OpenGL 3.3 not supported";
}
有几点值得一提：
1。尽管我知道不建议这样做，但 SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE, 1) 也可以
2。在 SDL2 中，SDL_GL_SetAttribute SDL_GL_MULTISAMPLESAMPLES 对我来说上升到 16，在 glewInit() 失败之后，但是，在 window 创建之后移动多重采样设置，然后 glewInit 突然停止抱怨：我的猜测是它只是被忽略了。
3。在 SDL1.2 中，Multisampling "seem" 的任何值都可以工作
4。考虑到模板缓冲区功能，只有下面的代码也可以工作，但我 post 它本质上是为了提出一个问题：有多少属性设置在实际工作？以及如何知道，因为代码编译并且 运行s 没有明显的问题？
// PROBABLY WRONG:
// ----
SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE, 8);
const SDL_VideoInfo * i;
if((i = SDL_GetVideoInfo()) == NULL)
{
throw "Video query failed";
}
int flag = (fs ? SDL_OPENGL | SDL_FULLSCREEN : SDL_OPENGL);
if(SDL_SetVideoMode(w, h, i->vfmt->BitsPerPixel, flag) == 0)
{
throw "Video mode set failed";
}
// No idea if the below is actually applied!
SDL_GL_SetAttribute(SDL_GL_RED_SIZE, 5);
SDL_GL_SetAttribute(SDL_GL_GREEN_SIZE, 5);
SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE, 5);
SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24);
SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
SDL_GL_SetAttribute(SDL_GL_MULTISAMPLEBUFFERS, 1);
SDL_GL_SetAttribute(SDL_GL_MULTISAMPLESAMPLES, 16);
SDL_GL_SetAttribute(SDL_GL_ACCELERATED_VISUAL, 1);