@ -29,6 +29,8 @@
* @ brief Function @ ref Magnum : : TextureTools : : distanceField ( )
*/
# include <memory>
# include "Magnum/configure.h"
# ifdef MAGNUM_TARGET_GL
@ -42,37 +44,29 @@
namespace Magnum { namespace TextureTools {
/**
@ brief Create signed distance field
@ param input Input texture
@ param output Output texture
@ param rectangle Rectangle in output texture where to render
@ param radius Max lookup radius in input texture
@ param imageSize Input texture size . Needed only in OpenGL ES , in desktop
OpenGL the information is gathered automatically using
@ ref GL : : Texture2D : : imageSize ( ) .
Converts binary image ( stored in red channel of @ p input ) to signed distance
field ( stored in red channel in @ p rectangle of @ p output ) . The purpose of this
function is to convert high - resolution binary image ( such as vector artwork or
font glyphs ) to low - resolution grayscale image . The image will then occupy much
less memory and can be scaled without aliasing issues . Additionally it provides
foundation for features like outlining , glow or drop shadow essentially for
free .
@ brief Create a signed distance field
Converts a binary black / white image ( stored in the red channel of @ p input ) to
a signed distance field ( stored in the red channel of @ p output @ p rectangle ) .
The purpose of this function is to convert a high - resolution binary image ( such
as vector artwork or font glyphs ) to a low - resolution grayscale image . The
image will then occupy much less memory and can be scaled without aliasing
issues . Additionally it provides foundation for features like outlining , glow
or drop shadow essentially for free .
You can also use the @ ref magnum - distancefieldconverter " magnum-distancefieldconverter "
utility to do distance field conversion on command - line . By extension , this
functionality is also provided through @ ref magnum - fontconverter " magnum-fontconverter "
utility .
utility to do distance field conversion on command - line . This functionality is
also used inside the @ ref magnum - fontconverter " magnum-fontconverter " utility .
# ## The algorithm
@ section TextureTools - DistanceField - algorithm The algorithm
For each pixel inside @ p rectangle the algorithm looks at corresponding pixel in
@ p input and tries to find nearest pixel of opposite color in area given by
@ p radius . Signed distance between the points is then saved as value of giv en
pixel in @ p output . Value of 1.0 means that the pixel was originally colored
white and nearest black pixel is farther than @ p radius , value of 0.0 means
that the pixel was originally black and nearest white pixel is farther than
@ p radius . Values around 0.5 are around edges .
For each pixel inside the @ p output sub - rectangle the algorithm looks at
corresponding pixel in the input and tries to find nearest pixel of opposite
color in an area defined @ p radius . Signed distance between the points is then
saved as value of given pixel in @ p output . Value of 1.0 means that the pixel
was originally colored w hite and nearest black pixel is farther than @ p radius ,
value of 0.0 means that the pixel was originally black and nearest white pixel
is farther than @ p radius . Values around 0.5 are around edges .
The resulting texture can be used with bilinear filtering . It can be converted
back to binary form in shader using e . g . GLSL @ glsl smoothstep ( ) @ ce function
@ -84,13 +78,14 @@ Based on: *Chris Green - Improved Alpha-Tested Magnification for Vector Textures
and Special Effects , SIGGRAPH 2007 ,
http : //www.valvesoftware.com/publications/2007/SIGGRAPH2007_AlphaTestedMagnification.pdf*
@ attention This is GPU - only implementation , so it expects active context .
@ attention This is a GPU - only implementation , so it expects an active GL
context .
@ note If internal format of @ p output texture is not renderable , this function
prints message to error output and does nothing . I ndesktop OpenGL and
OpenGL ES 3.0 it ' s common to render to @ ref GL : : TextureFormat : : R8 . I n
prints a message to error output and does nothing . O ndesktop OpenGL and
OpenGL ES 3.0 it ' s common to render to @ ref GL : : TextureFormat : : R8 . O n
OpenGL ES 2.0 you can use @ ref GL : : TextureFormat : : Red if
@ gl_extension { EXT , texture_rg } is available , if not , the smallest but still
@ gl_extension { EXT , texture_rg } is available ; if not , the smallest but still
inefficient supported format is in most cases @ ref GL : : TextureFormat : : RGB ,
rendering to @ ref GL : : TextureFormat : : Luminance is not supported in most
cases .
@ -102,10 +97,54 @@ http://www.valvesoftware.com/publications/2007/SIGGRAPH2007_AlphaTestedMagnifica
@ bug ES ( and maybe GL < 3.20 ) implementation behaves slightly different
( jaggies , visible e . g . when rendering outlined fonts )
*/
# ifndef MAGNUM_TARGET_GLES
void MAGNUM_TEXTURETOOLS_EXPORT distanceField ( GL : : Texture2D & input , GL : : Texture2D & output , const Range2Di & rectangle , Int radius , const Vector2i & imageSize = Vector2i ( ) ) ;
# else
void MAGNUM_TEXTURETOOLS_EXPORT distanceField ( GL : : Texture2D & input , GL : : Texture2D & output , const Range2Di & rectangle , Int radius , const Vector2i & imageSize ) ;
class MAGNUM_TEXTURETOOLS_EXPORT DistanceField {
public :
/**
* @ brief Constructor
* @ param radius Max lookup radius in the input texture
*
* Prepares the shader and other internal state for given @ p radius .
*/
explicit DistanceField ( UnsignedInt radius ) ;
~ DistanceField ( ) ;
/** @brief Max lookup radius */
UnsignedInt radius ( ) const ;
/**
* @ brief Calculate the distance field
* @ param input Input texture
* @ param output Output texture
* @ param rectangle Rectangle in output texture where to render
* @ param imageSize Input texture size . Needed only for OpenGL ES ,
* on desktop GL the information is gathered automatically using
* @ ref GL : : Texture2D : : imageSize ( ) .
*/
void operator ( ) ( GL : : Texture2D & input , GL : : Texture2D & output , const Range2Di & rectangle , const Vector2i & imageSize
# ifndef MAGNUM_TARGET_GLES
= { }
# endif
) ;
private :
struct State ;
std : : unique_ptr < State > _state ;
} ;
# ifdef MAGNUM_BUILD_DEPRECATED
/**
@ brief Create a signed distance field
@ deprecated Deprecated due to inefficiency of its statelessness when doing
batch processing . Use the @ ref DistanceField class instead .
*/
inline CORRADE_DEPRECATED ( " use the DistanceField class instead " ) void distanceField ( GL : : Texture2D & input , GL : : Texture2D & output , const Range2Di & rectangle , Int radius , const Vector2i & imageSize
# ifndef MAGNUM_TARGET_GLES
= Vector2i { }
# endif
) {
DistanceField { UnsignedInt ( radius ) } ( input , output , rectangle , imageSize ) ;
}
# endif
} }
Vladimír Vondruš
8 years ago