/usr/share/doc/libplplot12/examples/c/x30c.c is in libplplot-dev 5.10.0+dfsg-1.
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// Alpha color values demonstration.
//
// Copyright (C) 2008 Hazen Babcock
//
//
// This file is part of PLplot.
//
// PLplot is free software; you can redistribute it and/or modify
// it under the terms of the GNU Library General Public License as published
// by the Free Software Foundation; either version 2 of the License, or
// (at your option) any later version.
//
// PLplot is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Library General Public License for more details.
//
// You should have received a copy of the GNU Library General Public License
// along with PLplot; if not, write to the Free Software
// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
//
// This example will only really be interesting when used with devices that
// support or alpha (or transparency) values, such as the cairo device family.
//
#include "plcdemos.h"
static PLINT red[] = { 0, 255, 0, 0 };
static PLINT green[] = { 0, 0, 255, 0 };
static PLINT blue[] = { 0, 0, 0, 255 };
static PLFLT alpha[] = { 1.0, 1.0, 1.0, 1.0 };
static PLFLT px[] = { 0.1, 0.5, 0.5, 0.1 };
static PLFLT py[] = { 0.1, 0.1, 0.5, 0.5 };
static PLFLT pos[] = { 0.0, 1.0 };
static PLFLT rcoord[] = { 1.0, 1.0 };
static PLFLT gcoord[] = { 0.0, 0.0 };
static PLFLT bcoord[] = { 0.0, 0.0 };
static PLFLT acoord[] = { 0.0, 1.0 };
static PLBOOL rev[] = { 0, 0 };
int
main( int argc, const char *argv[] )
{
int i, j;
PLINT icol, r, g, b;
PLFLT a;
plparseopts( &argc, argv, PL_PARSE_FULL );
plinit();
plscmap0n( 4 );
plscmap0a( red, green, blue, alpha, 4 );
//
// Page 1:
//
// This is a series of red, green and blue rectangles overlaid
// on each other with gradually increasing transparency.
//
// Set up the window
pladv( 0 );
plvpor( 0.0, 1.0, 0.0, 1.0 );
plwind( 0.0, 1.0, 0.0, 1.0 );
plcol0( 0 );
plbox( "", 1.0, 0, "", 1.0, 0 );
// Draw the boxes
for ( i = 0; i < 9; i++ )
{
icol = i % 3 + 1;
// Get a color, change its transparency and
// set it as the current color.
plgcol0a( icol, &r, &g, &b, &a );
plscol0a( icol, r, g, b, 1.0 - (double) i / 9.0 );
plcol0( icol );
// Draw the rectangle
plfill( 4, px, py );
// Shift the rectangles coordinates
for ( j = 0; j < 4; j++ )
{
px[j] += 0.5 / 9.0;
py[j] += 0.5 / 9.0;
}
}
//
// Page 2:
//
// This is a bunch of boxes colored red, green or blue with a single
// large (red) box of linearly varying transparency overlaid. The
// overlaid box is completely transparent at the bottom and completely
// opaque at the top.
//
// Set up the window
pladv( 0 );
plvpor( 0.1, 0.9, 0.1, 0.9 );
plwind( 0.0, 1.0, 0.0, 1.0 );
// Draw the boxes. There are 25 of them drawn on a 5 x 5 grid.
for ( i = 0; i < 5; i++ )
{
// Set box X position
px[0] = 0.05 + 0.2 * i;
px[1] = px[0] + 0.1;
px[2] = px[1];
px[3] = px[0];
// We don't want the boxes to be transparent, so since we changed
// the colors transparencies in the first example we have to change
// the transparencies back to completely opaque.
icol = i % 3 + 1;
plgcol0a( icol, &r, &g, &b, &a );
plscol0a( icol, r, g, b, 1.0 );
plcol0( icol );
for ( j = 0; j < 5; j++ )
{
// Set box y position and draw the box.
py[0] = 0.05 + 0.2 * j;
py[1] = py[0];
py[2] = py[0] + 0.1;
py[3] = py[2];
plfill( 4, px, py );
}
}
// Create the color map with 128 colors and use plscmap1la to initialize
// the color values with a linearly varying red transparency (or alpha)
plscmap1n( 128 );
plscmap1la( 1, 2, pos, rcoord, gcoord, bcoord, acoord, rev );
// Use that cmap1 to create a transparent red gradient for the whole
// window.
px[0] = 0.;
px[1] = 1.;
px[2] = 1.;
px[3] = 0.;
py[0] = 0.;
py[1] = 0.;
py[2] = 1.;
py[3] = 1.;
plgradient( 4, px, py, 90. );
plend();
exit( 0 );
}
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