Demos (master): line-xor: test line drawing in XOR mode

[Brian Paul]

Module: Demos
Branch: master
Commit: 880241540635b308a4f8adc7b8cb4cbf500546a2
URL:    http://cgit.freedesktop.org/mesa/demos/commit/?id=880241540635b308a4f8adc7b8cb4cbf500546a2

Author: Brian Paul <brianp at vmware.com>
Date:   Thu Oct  7 09:19:07 2010 -0600

line-xor: test line drawing in XOR mode

Also good for checking that the last pixel of a line is not drawn (so that
we don't hit pixels twice at the vertex of connected lines).

---

 src/trivial/Makefile.am |    1 +
 src/trivial/line-xor.c  |  128 +++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 129 insertions(+), 0 deletions(-)

diff --git a/src/trivial/Makefile.am b/src/trivial/Makefile.am
index ec87c45..4e2d389 100644
--- a/src/trivial/Makefile.am
+++ b/src/trivial/Makefile.am
@@ -75,6 +75,7 @@ bin_PROGRAMS = \
 	line-userclip-nop \
 	line-userclip-nop-clip \
 	line-wide \
+	line-xor \
 	long-fixed-func \
 	pgon-mode \
 	point \
diff --git a/src/trivial/line-xor.c b/src/trivial/line-xor.c
new file mode 100644
index 0000000..72c08a5
--- /dev/null
+++ b/src/trivial/line-xor.c
@@ -0,0 +1,128 @@
+/*
+ * Draw lines in XOR mode.
+ * Note that the last pixel in a line segment should not be drawn by GL
+ * so that pixels aren't touched twice at the shared vertex of connected lines.
+ *
+ * Brian Paul
+ * 7 Oct 2010
+ */
+
+
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include <GL/glut.h>
+
+
+static GLboolean xor = GL_TRUE;
+
+
+static void
+Reshape(int width, int height)
+{
+   glViewport(0, 0, (GLint)width, (GLint)height);
+
+   glMatrixMode(GL_PROJECTION);
+   glLoadIdentity();
+   glOrtho(-1.0, 1.0, -1.0, 1.0, -1.0, 1.0);
+   glMatrixMode(GL_MODELVIEW);
+}
+
+
+static void 
+Key(unsigned char key, int x, int y)
+{
+   if (key == 'x') {
+      xor = !xor;
+      printf("XOR mode: %s\n", xor ? "on" : "off");
+   }
+   else if (key == 27)
+      exit(0);
+   glutPostRedisplay();
+}
+
+
+static void
+Draw(void)
+{
+   glClear(GL_COLOR_BUFFER_BIT); 
+
+   glLogicOp(GL_XOR);
+   if (xor)
+      glEnable(GL_COLOR_LOGIC_OP);
+   else
+      glDisable(GL_COLOR_LOGIC_OP);
+
+   glColor3f(0, 1, 0);
+
+   /* outer line rect */
+   glBegin(GL_LINE_LOOP);
+   glVertex2f(-0.9, -0.9);
+   glVertex2f( 0.9, -0.9);
+   glVertex2f( 0.9,  0.9);
+   glVertex2f(-0.9,  0.9);
+   glEnd();
+
+   /* middle line rect */
+   glBegin(GL_LINE_STRIP);
+   glVertex2f(-0.8, -0.8);
+   glVertex2f( 0.8, -0.8);
+   glVertex2f( 0.8,  0.8);
+   glVertex2f(-0.8,  0.8);
+   glVertex2f(-0.8, -0.8);
+   glEnd();
+
+   /* inner line rect */
+   glBegin(GL_LINES);
+   glVertex2f(-0.7, -0.7);
+   glVertex2f( 0.7, -0.7);
+
+   glVertex2f( 0.7, -0.7);
+   glVertex2f( 0.7,  0.7);
+
+   glVertex2f( 0.7,  0.7);
+   glVertex2f(-0.7,  0.7);
+
+   glVertex2f(-0.7,  0.7);
+   glVertex2f(-0.7, -0.7);
+   glEnd();
+
+   /* inner + pattern */
+   glBegin(GL_LINES);
+   glVertex2f(-0.6,  0.0);
+   glVertex2f( 0.6,  0.0);
+   glVertex2f( 0.0,  0.6);
+   glVertex2f( 0.0, -0.6);
+   glEnd();
+
+
+   glutSwapBuffers();
+}
+
+
+int
+main(int argc, char **argv)
+{
+   glutInit(&argc, argv);
+
+   glutInitWindowSize(250, 250);
+
+   glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE);
+   glutCreateWindow(argv[0]);
+   glutReshapeFunc(Reshape);
+   glutKeyboardFunc(Key);
+   glutDisplayFunc(Draw);
+
+   fprintf(stderr, "GL_RENDERER   = %s\n", (char *) glGetString(GL_RENDERER));
+   fprintf(stderr, "GL_VERSION    = %s\n", (char *) glGetString(GL_VERSION));
+   fprintf(stderr, "GL_VENDOR     = %s\n", (char *) glGetString(GL_VENDOR));
+   fprintf(stderr, "NOTE: there should be no pixels missing at the corners"
+           " of the line loops.\n");
+   fprintf(stderr, "There should be a missing pixel at the center of the '+'.\n");
+   fprintf(stderr, "Resize the window to check for any pixel drop-outs.\n");
+   fprintf(stderr, "Press 'x' to toggle XOR mode on/off.\n");
+
+   glutMainLoop();
+
+   return 0;
+}