I already opened a thread on this topic ("Could FLTK manage color
transparency?") and Ian tried to help me, but, maybe for my bad and confuse
English, it stopped immediately.
So I retry and hope to be more precise:
1) Is there a way to use transparent (alpha-blended) colors in a
Fl_Widget::draw() method? I read in the doc ("Drawing things in FLTK"):
"FLTK manages colors as 32-bit unsigned integers. Values from 0 to 255
represent colors from the FLTK 1.0.x standard colormap ...
Color values greater than 255 are treated as 24-bit RGB values..."
Then, if I understood, I can choose between a (solid) color-mapped or a RGB
color (still solid: the fourth byte is ignored) and I can not, for example, get
a Fl_Box with a semi-transparent background color.
Is this correct?
2) I was able to get semi-transparent rectangles using Fl_RGB_Image class (see
code below). It works, but there is much flickering with big rectangles.
Then I ask: is there a better way to achieve the same result (without, of
course, wasting memory with a 1600 x 1200 buffer ...)?
Thanks N. Cassetta
//*********************************************************
#include <cmath>
#include <FL/Fl.H>
#include <Fl/Fl_Box.H>
#include <FL/Fl_Overlay_Window.H>
#include <FL/Fl_Image.H>
#include <FL/Fl_draw.H>
// **************** the translucent box
const Fl_Color ALPHA_COLOR = (Fl_Color)0x80400080;
class SelectionRect : public Fl_RGB_Image {
public:
SelectionRect(int W, int H, Fl_Color c =
ALPHA_COLOR);
// W and H are the buffer dimensionse
void draw(int X, int Y, int W, int H);
private:
Fl_Color col;
unsigned char* buffer;
};
SelectionRect::SelectionRect(int W, int H, Fl_Color c) :
Fl_RGB_Image(buffer = new unsigned char[4*W*H], W, H, 4), col(c) {
int len = W * H;
Fl_Color* p = (Fl_Color *)buffer;
for (int i = 0; i < len; i++, p++) //fills the buffer
*p = col;
}
void SelectionRect::draw(int X, int Y, int W, int H) {
// this is like Fl_Tiled_Image drawing
fl_push_clip(X, Y, W, H);
int xtimes = W / w();
int ytimes = H / h();
for(int j = 0; j <= ytimes; j++)
for (int i = 0; i <= xtimes; i++)
Fl_RGB_Image::draw(X + i * w(), Y + j * h());
fl_rect(X, Y, W, H);
fl_pop_clip();
}
// ************** the main window
class MainWindow : public Fl_Overlay_Window {
public:
MainWindow();
virtual void draw_overlay();
virtual int handle(int e);
private:
int min(int a,int b) { return a < b ? a : b ; }
Fl_Box* MyBox;
SelectionRect* SelRect;
int xbegin, ybegin, xend, yend;
};
MainWindow::MainWindow(): Fl_Overlay_Window(100, 100, 600, 300) {
MyBox = new Fl_Box(100, 50, 400, 200, "Try to click and draw!");
// only for demonstrate trasparency
MyBox->box(FL_UP_BOX);
MyBox->align(FL_ALIGN_INSIDE | FL_ALIGN_WRAP);
MyBox->labelsize(60);
end();
SelRect = new SelectionRect(100, 100);
};
void MainWindow::draw_overlay() {
int x = min(xbegin, xend), y = min(ybegin, yend);
int w = fabs(xbegin - xend), h = fabs(ybegin - yend);
SelRect->draw(x, y, w, h);
}
int MainWindow::handle(int e) {
switch(e) {
case FL_PUSH:
xbegin = xend = Fl::event_x();
ybegin = yend = Fl::event_y();
break;
case FL_DRAG:
xend = Fl::event_x();
yend = Fl::event_y();
break;
case FL_RELEASE:
break;
default:
return 0;
}
redraw_overlay();
return 1;
}
// ************************** the main()
int main()
{
MainWindow* mwin = new MainWindow ();
mwin->show();
return Fl::run();
}
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