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I've noticed that the OpenVG transformation matrix is ignored by the text rendering routine at all and I cannot control the text position with it manually with VG_GLYPH_ORIGIN parameter.

I'm implementing a scene graph. I found out that I can use vgGetMatrix, read components 6 and 7 of the current 3x3 transform matrix and set VG_GLYPH_ORIGIN to those values before drawing a block of text. This allows the text origin to be placed in correct place, but the text is still always displayed left-to-right.

However, this itself doesn't enable me to do any other transformations, like rotation. I'm surprised because the text is composed from VGPaths and they are indeed transformed

Is there a way to make the text rotated with OpenVG 1.1? Or should I ignore the text functionality from OpenVG 1.1 and draw the letters as individual paths or images manually?

Kos
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1 Answers1

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All the draw functions use a different user->surface matrix:

  • vgDrawPath uses VG_MATRIX_PATH_USER_TO_SURFACE
  • vgDrawImage uses VG_MATRIX_IMAGE_USER_TO_SURFACE
  • vgDrawGlyph/vgDrawGlyphs use VG_MATRIX_GLYPH_USER_TO_SURFACE

By default, all of the matrix functions (vgTranslate, vgRotate, vgLoadMatrix, etc) operate on VG_MATRIX_PATH_USER_TO_SURFACE. To change the active matrix, call vgSeti with VG_MATRIX_MODE as the first argument:

vgSeti(VG_MATRIX_MODE, VG_MATRIX_GLYPH_USER_TO_SURFACE);
/* now vgTranslate, vgRotate, etc will operate on VG_MATRIX_GLYPH_USER_TO_SURFACE */
dave
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