How to change the label positioning in a Fl_Box? - c++

Question

I want to customize the label position inside a Fl_Box. Looking at the documentation I saw the draw_label() function here: this is a protected member of Fl_Widget, hence I derived a custom class for Fl_Box. The code is below.
#include <FL/Fl.H>
#include <FL/Fl_Window.H>
#include <FL/Fl_Box.H>
#include <FL/Fl_Button.H>
class mBox: public Fl_Box{
public:
mBox(int X, int Y, int W, int H, const char* l=0): Fl_Box(X,Y,W,H,l){};
void drawLabel(){
label("New");
draw_label(x(),y(),100,25);
redraw_label();
};
};
void action(Fl_Widget* w, void* data){
mBox* B = (mBox*) data;
B -> drawLabel(); }
int main(int argc, char **argv) {
Fl_Window* G_win;
G_win = new Fl_Window(180,100,"The font test");
mBox* A = new mBox(10,10,110,50,"The font TEST.");
A -> box(FL_UP_BOX);
Fl_Button* b = new Fl_Button(10,70,100,25,"Test");
b -> callback(action,A);
G_win->show();
return(Fl::run()); }
When the button is pressed, I expect that the label in the box changes to "New" in the new bounding box whose left corner is at position x(), y() and its width and height are 110 and 50 (the dimension of the box), respectively. I call the redraw_label() function to force the drawing with the new bounding box. For what I understood, the new label should be in the top left corner of the box.
But what actually happens is that the new label is indeed "New", but its position is not changed. What am I missing here?
This question is a follow-up of this previous question: I am trying to understand how to change the position of the label with default font and then try to customize the position using non standard fonts.

Answer 1

The draw_label() method is intended to be used in the draw() method. If you want to trigger a draw based on a callback, this is a modification of your code:
#include <FL/Enumerations.H>
#include <FL/Fl.H>
#include <FL/Fl_Box.H>
#include <FL/Fl_Button.H>
#include <FL/Fl_Window.H>
#include <FL/fl_draw.H>
class mBox : public Fl_Box {
bool triggered = false;
public:
mBox(int X, int Y, int W, int H, const char* l = 0)
: Fl_Box(X, Y, W, H, l) {};
void drawLabel() {
triggered = true;
label("New");
};
void draw() override {
Fl_Box::draw();
if (triggered) {
fl_draw_box(box(), x(), y(), w(), h(), FL_BACKGROUND_COLOR);
draw_label(x(), y(), 100, 25);
}
}
};
void action(Fl_Widget* w, void* data) {
mBox* B = (mBox*)data;
B->drawLabel();
}
int main(int argc, char** argv) {
Fl_Window* G_win;
G_win = new Fl_Window(180, 100, "The font test");
mBox* A = new mBox(10, 10, 110, 50, "The font TEST.");
A->box(FL_UP_BOX);
Fl_Button* b = new Fl_Button(10, 70, 100, 25, "Test");
b->callback(action, A);
G_win->show();
return (Fl::run());
}

Answer 2

Although the previous answer has been accepted I'd like to share some thoughts and code to answer the text alignment question in general. If you want to align text precisely I suggest to use fl_draw() directly to draw the box label text aligned as required rather than using draw_label(). The following code does this in the draw() method of the derived class:
#include <FL/Fl.H>
#include <FL/Fl_Window.H>
#include <FL/Fl_Box.H>
#include <FL/Fl_Button.H>
#include <FL/fl_draw.H>
class mBox : public Fl_Box {
public:
mBox(int X, int Y, int W, int H, const char *l = 0)
: Fl_Box(X, Y, W, H, l){};
void draw() {
draw_box();
// arbitrary text position, change this as you need
int xo = x() + 4;
int yo = y() + h() * 2 / 3;
// measure the text extents
int dx = 0, dy = 0, tw = 0, th = 0;
fl_font(labelfont(), labelsize());
fl_text_extents(label(), dx, dy, tw, th);
// draw the green base line
fl_color(FL_GREEN);
fl_xyline(xo, yo, xo + w() - 8);
// draw the text aligned to the green base line
fl_color(labelcolor());
fl_draw(label(), x() + (w()-tw)/2, yo);
}
};
void action(Fl_Widget *w, void *data) {
mBox *B = (mBox *)data;
B->label("New");
B->redraw();
}
int main(int argc, char **argv) {
Fl_Window *G_win;
G_win = new Fl_Window(510, 150, "The font test");
mBox *A1 = new mBox(10, 10, 240, 40, "Quick fox jumps over lazy dog.");
A1->box(FL_UP_BOX);
Fl_Box *A2 = new Fl_Box(260, 10, 240, 40, "Quick fox jumps over lazy dog.");
A2->box(FL_UP_BOX);
Fl_Button *b = new Fl_Button(10, 110, 100, 25, "Test");
b->callback(action, A1);
G_win->show();
return (Fl::run());
}
I modified the callback to set the label text and call redraw(). Everything else is done in draw().
I also added a standard Fl_Box widget to show the difference.