使用OpenVG旋转文字

Question

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 VGPath s 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?

Answer 1

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 */