3D Text's transparent areas will occlude objects drawn behind it afterwards. #29804

New Issue

kanttori · 2012-01-05T20:38:13+01:00

kanttori commented

2012-01-05 20:38:13 +01:00

Category: Rendering

%%%So the issue is following in the file attached:

Texts write depth and have depth test on. This means texts drawn behind another text will be occluded by the transparent part and at certain angles letters in same text to have z-fighting issues where they overlap (should occur between T and e).

One solution would be to disable blending when drawing 3d text in bge and enable opengl's alpha test to only allow alpha == 1.0 or alpha > limit.

No nice soft edges, but should always draw correctly.

Another way is to draw texts with other transparents ordered back to front; can be done without depth write so no z-fighting between letters in same text and can use blending on.

When z-ordering fails can still cause visual glitches (absolute perfection would require partitioning faces since face A can be partly behind and partly in front of face B.. gets complicated fast).%%%

**Category**: Rendering %%%So the issue is following in the file attached: Texts write depth and have depth test on. This means texts drawn behind another text will be occluded by the transparent part and at certain angles letters in same text to have z-fighting issues where they overlap (should occur between T and e). One solution would be to disable blending when drawing 3d text in bge and enable opengl's alpha test to only allow alpha == 1.0 or alpha > limit. - > No nice soft edges, but should always draw correctly. Another way is to draw texts with other transparents ordered back to front; can be done without depth write so no z-fighting between letters in same text and can use blending on. - > When z-ordering fails can still cause visual glitches (absolute perfection would require partitioning faces since face A can be partly behind and partly in front of face B.. gets complicated fast).%%%

kanttori commented

2012-01-05 20:38:13 +01:00

Changed status to: 'Open'

kanttori commented

2012-01-07 08:05:29 +01:00

%%%Meh, I was probably overthinking this by a mile. True, after alphatest the remaining transparent areas will suffer from blending against wrong colors but in the end it is just the edge pixels and most visible when the text is being magnified. This can be minimized by using a higher alpha to test against which will only leave the texture pixels that influence the resulting color more.

Index: source/gameengine/BlenderRoutines/KX_BlenderGL.cpp

- source/gameengine/BlenderRoutines/KX_BlenderGL.cpp	(revision 43202)

+++ source/gameengine/BlenderRoutines/KX_BlenderGL.cpp (working copy)
@@ -147,8 +147,15 @@

BLF_size(fontid, size, dpi);
BLF_position(fontid, 0, 0, 0);

/* Use alphatest to prune transparent areas */
glEnable(GL_ALPHA_TEST);
glAlphaFunc(GL_GREATER, 0.5f);
BLF_draw(fontid, (char *)text, strlen(text));
glDisable(GL_ALPHA_TEST);
BLF_disable(fontid, BLF_MATRIX|BLF_ASPECT);
}

%%%

%%%Meh, I was probably overthinking this by a mile. True, after alphatest the remaining transparent areas will suffer from blending against wrong colors but in the end it is just the edge pixels and most visible when the text is being magnified. This can be minimized by using a higher alpha to test against which will only leave the texture pixels that influence the resulting color more. Index: source/gameengine/BlenderRoutines/KX_BlenderGL.cpp **** - source/gameengine/BlenderRoutines/KX_BlenderGL.cpp (revision 43202) +++ source/gameengine/BlenderRoutines/KX_BlenderGL.cpp (working copy) @@ -147,8 +147,15 @@ BLF_size(fontid, size, dpi); BLF_position(fontid, 0, 0, 0); + + /* Use alphatest to prune transparent areas */ + glEnable(GL_ALPHA_TEST); + glAlphaFunc(GL_GREATER, 0.5f); + BLF_draw(fontid, (char *)text, strlen(text)); + glDisable(GL_ALPHA_TEST); + BLF_disable(fontid, BLF_MATRIX|BLF_ASPECT); } %%%

Dalai Felinto commented

2012-01-09 21:28:57 +01:00

%%%Hi Juha,

GL_ALPHA_TEST is explicitly disabled in the DisableText routine.
This was added in revision 15867. Log here for convenience:

Game Engine: alpha blending and sorting

Alpha blending + sorting was revised, to fix bugs and get it to work more predictable.

A new per texture face "Sort" setting defines if the face is alpha sorted or not, instead of abusing the "ZTransp" setting as it did before.
Existing files are converted to hopefully match the old behavior as much as possible with a version patch.
On new meshes the Sort flag is disabled by the default, to avoid unexpected and hard to find slowdowns.
Alpha sorting for faces was incredibly slow. Sorting faces in a mesh with 600 faces lowered the framerate from 200 to 70 fps in my test.. the sorting there case goes about 15x faster now, but it is still advised to use Clip Alpha if possible instead of regular Alpha.
There still various limitations in the alpha sorting code, I've added some comments to the code about this.

The regular alpha routine in BGE is handled inside the GPU_set_material_alpha_blend%%%

%%%Hi Juha, GL_ALPHA_TEST is explicitly disabled in the DisableText routine. This was added in revision 15867. Log here for convenience: **** Game Engine: alpha blending and sorting **** Alpha blending + sorting was revised, to fix bugs and get it to work more predictable. * A new per texture face "Sort" setting defines if the face is alpha sorted or not, instead of abusing the "ZTransp" setting as it did before. * Existing files are converted to hopefully match the old behavior as much as possible with a version patch. * On new meshes the Sort flag is disabled by the default, to avoid unexpected and hard to find slowdowns. * Alpha sorting for faces was incredibly slow. Sorting faces in a mesh with 600 faces lowered the framerate from 200 to 70 fps in my test.. the sorting there case goes about 15x faster now, but it is still advised to use Clip Alpha if possible instead of regular Alpha. * There still various limitations in the alpha sorting code, I've added some comments to the code about this. **** The regular alpha routine in BGE is handled inside the GPU_set_material_alpha_blend%%%

Dalai Felinto commented

2012-01-09 21:35:45 +01:00

%%%That said, it seems safe to set whatever opengl flag we need.
Alpha rendering always make sure the proper flags are set (see gpu_set_alpha_blend in ^/source/blender/gpu/intern/gpu_draw.c).%%%

%%%That said, it seems safe to set whatever opengl flag we need. Alpha rendering always make sure the proper flags are set (see gpu_set_alpha_blend in ^/source/blender/gpu/intern/gpu_draw.c).%%%

Diego Borghetti commented

2014-03-29 22:14:14 +01:00

Hello,

Yep, KX_BlenderGL.cpp file was remove in the cleanup. I tracked down the commit (point by Dalai) and found the DisableForText function.

So far using GL_ALPHA_TEST and GL_GREATER works fine, but should not this check if GL_ALPHA_TEST is not already enable ?
In the example file, GL_ALPHA_TEST is disable when the text is render, but if that is not the case, the GL_ALPHA_TEST will be disable when the RenderText3D call return.

I'm not sure how much will impact this in the GE (add a glIsEnable(GL_ALPHA_TEST at the start).

The patch looks like:
diff --git a/source/gameengine/Rasterizer/RAS_OpenGLRasterizer/RAS_OpenGLRasterizer.cpp b/source/gameengine/Rasterizer/RAS_OpenGLRasterizer/RAS_OpenGLRasterizer.cpp
index 1227fe8..caf5186 100644
- a/source/gameengine/Rasterizer/RAS_OpenGLRasterizer/RAS_OpenGLRasterizer.cpp
+++ b/source/gameengine/Rasterizer/RAS_OpenGLRasterizer/RAS_OpenGLRasterizer.cpp
@@ -1401,10 +1401,15 @@ void RAS_OpenGLRasterizer::applyTransform(double* oglmatrix,int objectdrawmode )

static void DisableForText()
{

```
  GLboolean alpha_test;
```

      glPolygonMode(GL_FRONT_AND_BACK, GL_FILL); /* needed for texture fonts otherwise they render as wireframe */

      glDisable(GL_BLEND);

glDisable(GL_ALPHA_TEST);

  alpha_test= glIsEnabled(GL_ALPHA_TEST);

```
  if (alpha_test == GL_FALSE)
```
```
          glEnable(GL_ALPHA_TEST);
```
```
  glAlphaFunc(GL_GREATER, 0.5f);
```

      glDisable(GL_LIGHTING);
      glDisable(GL_COLOR_MATERIAL);

@@ -1427,6 +1432,9 @@ static void DisableForText()

              glDisable(GL_TEXTURE_2D);
      }

```
  if (GL_ALPHA_TEST == GL_FALSE)
```
```
          glDisable(GL_ALPHA_TEST);
```

}

void RAS_OpenGLRasterizer::RenderBox2D(int xco,

@dfelinto any comment ?

Hello, Yep, KX_BlenderGL.cpp file was remove in the cleanup. I tracked down the commit (point by Dalai) and found the DisableForText function. So far using GL_ALPHA_TEST and GL_GREATER works fine, but should not this check if GL_ALPHA_TEST is not already enable ? In the example file, GL_ALPHA_TEST is disable when the text is render, but if that is not the case, the GL_ALPHA_TEST will be disable when the RenderText3D call return. I'm not sure how much will impact this in the GE (add a glIsEnable(GL_ALPHA_TEST at the start). The patch looks like: diff --git a/source/gameengine/Rasterizer/RAS_OpenGLRasterizer/RAS_OpenGLRasterizer.cpp b/source/gameengine/Rasterizer/RAS_OpenGLRasterizer/RAS_OpenGLRasterizer.cpp index 1227fe8..caf5186 100644 - a/source/gameengine/Rasterizer/RAS_OpenGLRasterizer/RAS_OpenGLRasterizer.cpp +++ b/source/gameengine/Rasterizer/RAS_OpenGLRasterizer/RAS_OpenGLRasterizer.cpp @@ -1401,10 +1401,15 @@ void RAS_OpenGLRasterizer::applyTransform(double* oglmatrix,int objectdrawmode ) static void DisableForText() { + GLboolean alpha_test; + ``` glPolygonMode(GL_FRONT_AND_BACK, GL_FILL); /* needed for texture fonts otherwise they render as wireframe */ ``` ``` glDisable(GL_BLEND); ``` - glDisable(GL_ALPHA_TEST); + alpha_test= glIsEnabled(GL_ALPHA_TEST); + if (alpha_test == GL_FALSE) + glEnable(GL_ALPHA_TEST); + glAlphaFunc(GL_GREATER, 0.5f); ``` glDisable(GL_LIGHTING); glDisable(GL_COLOR_MATERIAL); ``` @@ -1427,6 +1432,9 @@ static void DisableForText() ``` glDisable(GL_TEXTURE_2D); } ``` + + if (GL_ALPHA_TEST == GL_FALSE) + glDisable(GL_ALPHA_TEST); } void RAS_OpenGLRasterizer::RenderBox2D(int xco, @dfelinto any comment ?

Aaron Carlisle commented

2019-06-29 02:12:25 +02:00

Changed status from 'Open' to: 'Archived'

Aaron Carlisle closed this issue

2019-06-29 02:12:25 +02:00

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3D Text's transparent areas will occlude objects drawn behind it afterwards. #29804