Add gluArcball structure and support functions

This adds basic code to implement the class arcball user interface control.

3 files changed, 214 insertions, 1 deletions

diff --git a/include/glu3.h b/include/glu3.h
index 3d7a10b..f3cbfcf 100644
--- a/include/glu3.h
+++ b/include/glu3.h
@@ -215,10 +215,58 @@ struct GLUmat4Stack {
 #endif	/* __cplusplus */
 };
 
+
+struct GLUarcball {
+	/**
+	 * Base location of the viewport.
+	 */
+	/*@{*/
+	unsigned viewport_x;
+	unsigned viewport_y;
+	/*@}*/
+	
+	/**
+	 * Dimensions of the viewport.
+	 */
+	/*@{*/
+	unsigned viewport_width;
+	unsigned viewport_height;
+	/*@}*/
+
+	/**
+	 * Screen X/Y location of initial mouse click.
+	 */
+	/*@{*/
+	unsigned click_x;
+	unsigned click_y;
+	/*@}*/
+
+
+#ifdef __cplusplus
+	void viewport(unsigned x, unsigned y, unsigned width, unsigned height)
+	{
+		viewport_x = x;
+		viewport_y = y;
+		viewport_width = width;
+		viewport_height = height;
+	}
+
+	void click(unsigned x, unsigned y)
+	{
+		click_x = x;
+		click_y = y;
+	}
+
+	GLUmat4 drag(unsigned end_x, unsigned end_y);
+#endif	/* __cplusplus */
+};
+
+
 #ifndef __cplusplus
 typedef struct GLUvec4 GLUvec4;
 typedef struct GLUmat4 GLUmat4;
 typedef struct GLUmat4Stack GLUmat4Stack;
+typedef struct GLUarcball GLUarcball;
 #endif /*  __cplusplus */
 
 
@@ -681,6 +729,15 @@ extern const GLchar *gluLoadTextFile(const char *file_name);
  */
 extern void gluUnloadTextFile(const GLchar *text);
 
+extern void gluArcballViewport(GLUarcball *ball, unsigned x, unsigned y,
+    unsigned width, unsigned height);
+
+extern void gluArcballClick(GLUarcball *ball, unsigned start_x,
+    unsigned start_y);
+
+extern void gluArcballDrag(GLUarcball *ball, GLUmat4 *transformation,
+    unsigned end_x, unsigned end_y);
+
 #ifdef __cplusplus
 };
 #endif
@@ -972,6 +1029,14 @@ inline GLUmat4 gluInverse4(const GLUmat4 &m)
 	return result;
 }
 
+
+inline GLUmat4 GLUarcball::drag(unsigned end_x, unsigned end_y)
+{
+	GLUmat4 result;
+
+	gluArcballDrag(this, & result, end_x, end_y);
+	return result;
+}
 #endif /* __cplusplus */
 
 #include "glu3_scalar.h"
diff --git a/src/Makefile.am b/src/Makefile.am
index 9bd643c..6230523 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -24,7 +24,7 @@ AM_CXXFLAGS=-I../include
 AM_CFLAGS=-I../include
 
 lib_LIBRARIES = libGLU3.a
-libGLU3_a_SOURCES = matrix.c load_text.c
+libGLU3_a_SOURCES = matrix.c load_text.c arcball.c
 
 libGLU3includedir = ${includedir}
 libGLU3include_HEADERS = ../include/glu3.h ../include/glu3_scalar.h
diff --git a/src/arcball.c b/src/arcball.c
new file mode 100644
index 0000000..5c27d04
--- /dev/null
+++ b/src/arcball.c
@@ -0,0 +1,148 @@
+/*
+ * Copyright © 2009 Ian D. Romanick
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+#include <math.h>
+#include "glu3.h"
+
+
+static void
+map_to_sphere(float x, float y, GLUvec4 *v)
+{
+	const float length_squared = (x * x) + (y * y);
+
+
+	if (length_squared > 1.0f) {
+		const float n = 1.0f / sqrt(length_squared);
+
+		v->values[0] = x * n;
+		v->values[1] = y * n;
+		v->values[2] = 0.0f;
+	} else {
+		v->values[0] = x;
+		v->values[1] = y;
+		v->values[2] = sqrt(1.0 - length_squared);
+	}
+
+	v->values[3] = 0.0;
+}
+
+
+static float
+remap_x(float w_factor, unsigned x)
+{
+	return (x * w_factor) - 1.0f;
+}
+
+
+static float
+remap_y(float h_factor, unsigned y)
+{
+	return 1.0f - (y * h_factor);
+}
+
+
+static void
+get_transformation(GLUmat4 *mat, const GLUvec4 *quat)
+{
+	const float xx = quat->values[0] * quat->values[0];
+	const float xy = quat->values[0] * quat->values[1];
+	const float xz = quat->values[0] * quat->values[2];
+	const float xw = quat->values[0] * quat->values[3];
+
+	const float yy = quat->values[1] * quat->values[1];
+	const float yz = quat->values[1] * quat->values[2];
+	const float yw = quat->values[1] * quat->values[3];
+
+	const float zz = quat->values[2] * quat->values[2];
+	const float zw = quat->values[2] * quat->values[3];
+
+
+	mat->col[0].values[0] = 1.0f - 2.0f * (yy + zz);
+	mat->col[0].values[1] =        2.0f * (xy + zw);
+	mat->col[0].values[2] =        2.0f * (xz - yw);
+	mat->col[0].values[3] = 0.0f;
+
+	mat->col[1].values[0] =        2.0f * (xy - zw);
+	mat->col[1].values[1] = 1.0f - 2.0f * (xx + zz);
+	mat->col[1].values[2] =        2.0f * (yz + xw);
+	mat->col[1].values[3] = 0.0f;
+
+	mat->col[2].values[0] =        2.0f * (xz + yw);
+	mat->col[2].values[1] =        2.0f * (yz - xw);
+	mat->col[2].values[2] = 1.0f - 2.0f * (xx + yy);
+	mat->col[2].values[3] = 0.0f;
+
+	mat->col[3].values[0] = 0.0f;
+	mat->col[3].values[1] = 0.0f;
+	mat->col[3].values[2] = 0.0f;
+	mat->col[3].values[3] = 1.0f;
+}
+
+
+void
+gluArcballClick(GLUarcball *ball, unsigned x, unsigned y)
+{
+	ball->click_x = x;
+	ball->click_y = y;
+}
+
+
+void
+gluArcballDrag(GLUarcball *ball, GLUmat4 *result, unsigned x, unsigned y)
+{
+	GLUvec4 end;
+	GLUvec4 pick;
+	GLUvec4 axis;
+	float w_factor;
+	float h_factor;
+
+
+	if ((ball->viewport_width == 0.0) || (ball->viewport_height == 0.0)) {
+		memcpy(result, & gluIdentityMatrix, sizeof(gluIdentityMatrix));
+		return;
+	}
+
+	w_factor = 2.0f / (float)(ball->viewport_width  - 1);
+	h_factor = 2.0f / (float)(ball->viewport_height - 1);
+
+	map_to_sphere(remap_x(w_factor, ball->click_x - ball->viewport_x),
+		      remap_y(h_factor, ball->click_y - ball->viewport_y),
+		      & pick);
+	map_to_sphere(remap_x(w_factor, x - ball->viewport_x),
+		      remap_y(h_factor, y - ball->viewport_y),
+		      & end);
+
+
+	gluCross4v(& axis, & pick, & end);
+
+	const float length_squared = gluLengthSqr4v(& axis);
+	if (length_squared > 0.0000001) {
+		axis.values[3] = gluDot3_4v(& pick, & end);
+	} else {
+		axis.values[0] = 0.0f;
+		axis.values[1] = 0.0f;
+		axis.values[2] = 0.0f;
+		axis.values[3] = 0.0f;
+	}
+
+	get_transformation(result, & axis);
+}