GLUtessellator是否有强制使用GL_TRIANGLES的方法？

Question

我正在尝试使用GLUtesselator在OpenGL中生成3D挤出文本。以下是相关代码：

private boolean createText(final String displayText)
{
    final Font font = new Font("Times New Roman", Font.TRUETYPE_FONT, 3);
    final float depth = 1000f;
    final float flatness = 0.0001f;

    final GlyphVector glyphVector = font.createGlyphVector(
            new FontRenderContext(new AffineTransform(), true, true), new StringCharacterIterator(displayText));
    final GeneralPath generalPath = (GeneralPath) glyphVector.getOutline();
    final PathIterator pathIterator = generalPath.getPathIterator(AffineTransform.getScaleInstance(1.0, -1.0),
            flatness);

    tesselateFace(pathIterator, false, 0.0f);
    return false;
}

private void tesselateFace(final PathIterator pathIterator, final boolean justBoundary, final double tessZ)
{
    final GLUtessellatorCallback callback = new TessellatorCallback();
    final GLUtessellator tessellator = glu.gluNewTess();

    glu.gluTessCallback(tessellator, GLU.GLU_TESS_BEGIN, callback);
    glu.gluTessCallback(tessellator, GLU.GLU_TESS_END, callback);
    glu.gluTessCallback(tessellator, GLU.GLU_TESS_ERROR, callback);
    glu.gluTessCallback(tessellator, GLU.GLU_TESS_VERTEX, callback);
    glu.gluTessCallback(tessellator, GLU.GLU_TESS_COMBINE, callback);

    if (pathIterator.getWindingRule() == PathIterator.WIND_EVEN_ODD)
        glu.gluTessProperty(tessellator, GLU.GLU_TESS_WINDING_RULE, GLU.GLU_TESS_WINDING_ODD);
    else
        glu.gluTessProperty(tessellator, GLU.GLU_TESS_WINDING_RULE, GLU.GLU_TESS_WINDING_NONZERO);

    if (justBoundary)
        glu.gluTessProperty(tessellator, GLU.GLU_TESS_BOUNDARY_ONLY, GL.GL_TRUE);
    else
        glu.gluTessProperty(tessellator, GLU.GLU_TESS_BOUNDARY_ONLY, GL.GL_FALSE);

    glu.gluTessProperty(tessellator, GLU.GLU_TESS_EDGE_FLAG, GL.GL_TRUE);

    glu.gluTessBeginPolygon(tessellator, (double[]) null);

    while (!pathIterator.isDone())
    {
        final double[] coords = new double[3];
        coords[2] = tessZ;
        switch (pathIterator.currentSegment(coords))
        {
        case PathIterator.SEG_MOVETO:
            glu.gluTessBeginContour(tessellator);
            break;
        case PathIterator.SEG_LINETO:
            glu.gluTessVertex(tessellator, coords, 0, coords);
            break;
        case PathIterator.SEG_CLOSE:
            glu.gluTessEndContour(tessellator);
            break;
        }

        pathIterator.next();
    }
    glu.gluTessEndPolygon(tessellator);

    glu.gluDeleteTess(tessellator);
}

如果我相信第11章的RedBook，那么如果与GLU_TESS_EDGE_FLAG相关联的回调启用了边缘标志，则仅使用GL_TRIANGLES调用GLU_TESS_BEGIN回调。因此，我认为我应该只使用GL_TRIANGLES进行绘制。

然而，我可以看到在我的自定义曲面细分器回调中调用的类型可以是GL_TRIANGLE_FAN、GL_TRIANGLE_STRIP或GL_TRIANGLES中的任何一种。我只是想知道是否有一种方法可以强制执行这个，因为我太忙了，无法创建一个能处理除GL_QUADS或GL_TRIANGLES之外的任何其他东西的VBO。

- Sonoman

---

我发现你的函数有一个 Bug。在 PathIterator.SEG_MOVETO 情况下，你没有调用 GLU.gluTessVertex(tessellator, coords, 0, coords)。 - Vincent Cantin

Answer 1

我确定如果你只提供边缘回调函数（即使你什么也不做），那么你只会得到三角形。

我以前可能也遇到过同样的问题，并找到了这段代码和评论：

// providing this callback should stop triangle fans / strips coming back
if not fBoundaryOnly then
    gluTessCallback(tess, GLU_TESS_EDGE_FLAG_DATA, @tessEdgeData); 

Nb，这是Delphi代码，但仍然应该有意义。@tessEdgeData是指向回调例程的指针，该例程不执行任何操作。

- sergeantKK

Answer 2

sergeantKK的解决方案可行。

如果需要c++代码实现，代码如下：

void CALLBACK edgeCallback(void){return;}
gluTessCallback(Tobj, GLU_TESS_EDGE_FLAG_DATA,reinterpret_cast<_GLUfuncptr>(edgeCallback));

- Nayden Dochev