QGLText　核心绘制函数（用于Qt3D中文字显示） - QTCN开发网

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只看楼主倒序阅读楼主发表于: 2012-10-10

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/*-- Author: Xiao Long Teng , shared on 2012-10-10 --*/
void Geotech::QGLText::draw(QGLPainter *painter)
{
if (_str.isEmpty()) return;
QFontMetrics fm(_font);
QRect rect = fm.boundingRect(_str); // text bounding box
rect.adjust(0, 0, 1, 1);
QImage image(rect.size(), QImage::Format_ARGB32);
image.fill(0); // set to transparent
// draw the text on an image
QPainter p2d(&image);
p2d.setFont(_font);
p2d.setPen(QColor(_red * 255, _green * 255, _blue * 255, _alpha * 255));
p2d.drawText(0, 0, rect.width(), rect.height(), Qt::AlignCenter, _str);
p2d.end();
// convert the object coordinate to screen coordinate
GLdouble winx, winy, winz; // the screen coordinate of the object
QMatrix4x4 model = painter->modelViewMatrix().top();
QMatrix4x4 proj = painter->projectionMatrix().top();
QGLUtils::objectToWindowCoord(_x, _y, _z, model.data(),
proj.data(), &winx, &winy, &winz);
if (_alignW) winx -= rect.width()/2.0; // align center of width
if (_alignH) winy -= rect.height()/2.0; // align center of height
// define the font rectangle which is
// (x, y) (x + rect.width(), y)
// ------------------------------------
// | |
// | |
// ------------------------------------
// (x, y + rect.heigth()) (x + rect.width(), y + rect.heigth())
int x = (int)winx, y = (int)winy;
QVector2DArray vertices;
vertices.append(x, y + rect.height());
vertices.append(x, y);
vertices.append(x + rect.width(), y);
vertices.append(x + rect.width(), y + rect.height());
// texture coordinates
QVector2DArray texCoord;
texCoord.append(0.0f, 0.0f);
texCoord.append(0.0f, 1.0f);
texCoord.append(1.0f, 1.0f);
texCoord.append(1.0f, 0.0f);
// map the image to texture
QGLTexture2D texture;
texture.setImage(image);
// get viewport
GLint view[4];
glGetIntegerv(GL_VIEWPORT, &view[0]);
// use ortho projection to draw the text, because it
// is easy to find the position of the text under ortho projection.
// set projection matrix stack
painter->modelViewMatrix().push();
painter->modelViewMatrix().setToIdentity();
QMatrix4x4 projm;
// projm.ortho(QRect(view[0], view[1], view[2], view[3])); // Znear = -1.0, Zfar = 1.0
/**
* Description of glOrtho(left, right, bottom, top, nearVal, farVal) :
* (left, bottom, -nearVal) and (right, top, -nearVal) specify the points
* on the near clipping plane that are mapped to the lower left and upper
* right corners of the window.
*
* Note:
* -nearVal : specifies the location of the near clipping plane
* -farVal : specifies the location of the far clipping plane
*/
projm.ortho(view[0], view[2], view[3], view[1], 0, 1);
painter->projectionMatrix().push();
painter->projectionMatrix() = projm;
// move to the actual position from the screen origin
painter->modelViewMatrix().translate(0, 0, -winz);
// enable blend to make the background transaprecy of the text
glEnable(GL_BLEND);
// glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
painter->clearAttributes();
painter->setStandardEffect(QGL::FlatReplaceTexture2D);
texture.bind();
painter->setVertexAttribute(QGL::Position, vertices);
painter->setVertexAttribute(QGL::TextureCoord0, texCoord);
painter->draw(QGL::TriangleFan, 4);
painter->setStandardEffect(QGL::FlatColor);
glBindTexture(GL_TEXTURE_2D, 0);
glDisable(GL_BLEND);
// restore the matrix stack
painter->projectionMatrix().pop();
painter->modelViewMatrix().pop();
}