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The TextureTextLine allows to
display text that is rendered using textures instead of polygons. Thus, there
are only two textured triangles necessary for each letter.
Internally the TextureTextLine
node calculates an IndexedFaceSet
that contains one rectangular face for each letter of the string. The
texture coordinates of the faces point into a texture that contains a
bitmap for each letter of the font.
In contrast to
the standard VRML node Text, this
text is faster to render and can be better readable when the text
appears small, rotated or is viewed from the side if the texture uses large
character cells, e.g. 64x32 pixel per character.
This version of the TextureTextLine node
supports only fonts where each letter has the same width.
EXTERNPROTO TextureTextLine
[
exposedField SFString text # ""
exposedField SFVec2f size # .7 1
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exposedField SFString allign # "LEFT" or "CENTER" or "RIGHT"
field SFBool singleSided # TRUE
# configuration parameters that describe the font texture:
field SFFloat baseLine # .2
field SFInt32 firstChar # 32
field SFInt32 numCharsHorz # 16
field SFInt32 numCharsVert # 14
field SFInt32 imageWidth # 512
field SFInt32 imageHeight # 448
eventOut SFBool isLoaded
]
"TextureTextLine.wrl#TextureTextLine"
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To use this node, create a texture containing all letters you want to
display. They should look like these: OCR-1.5.png,
OCR-1.5-alpha.png. Create a
Shape node and assign
it the texture. The geometry
field receives a TextureTextLine
node.
Explanation of the fields:
exposedField SFString text ""
exposedField SFVec2f size .7 1
exposedField SFString allign "LEFT" or "CENTER" or "RIGHT"
The text field contains
the string that should be displayed by the node. This text is displayed
in the X-Y plane and is readable if viewed from a position with a
positive Z value.
The size of each letter is specified in the size
field. The field allign specifies
the allignment of the text: "LEFT" makes the origin (0, 0, 0) be on the left
edge of the left most letter, "RIGHT" makes the origin be on the right
edge of the right most letter, and "CENTER" makes it be in the center of the
text line.
field SFBool singleSided TRUE
Like with IndexedFaceSets
the text is only visible if viewed from the front. If you set this
flag to FALSE you can also see the text from behind it. But as a
mirrored text.
field SFFloat baseLine .2
This is the first parameter that describes the font in the texture.
It defines the distance from the bottom line of a cell for a letter to
the base line of the letter. The value is relative to the size of the
zell. I.e. it is in the range 0..1 .
field SFInt32 firstChar 32
field SFInt32 numCharsHorz 16
field SFInt32 numCharsVert 14
The texture is organized as a rectangular matrix of cells where each
cell contains the bitmap of one letter.
firstChar specifies the
integer code of the character in the top left cell.
numCharsHorz and
numCharsVert specify
the number of cells horizontally and vertically.
field SFInt32 imageWidth 512
field SFInt32 imageHeight 448
These two fields specify the size of the entire texture in pixels.
eventOut SFBool isLoaded
The VRML specification requires a VRML Browser to dispose all events
that a PROTO instance receives before it is loaded. IMHO this is a bad
idea, because it makes initializing a node with a value that is not
known at design time difficult. Therefore the
isLoaded field emits TRUE
when the PROTO has loaded.
The Demo:
This page displays some values about the current browser, time and
frame rate. It demonstrates that text can be changed on the fly.
Please rotate the text and change the distance to make it smaller
to see how and when the text is readable.
While modulating the foreground color by the
Material node
works in this example, modulating this, the background color
and the transparency may not work in all browsers/cases. :-(
__.-.__
end of document
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