[PATCH 2/5] kernel-shark-qt: Add basic instruments for OpenGL plotting.

["Yordan Karadzhov (VMware)" <y.karadz@gmail.com>]

This patch introduces tools for initializing OpenGL and for drawing
the three basic geometrical primitives (point, line and polygon)
used when plotting KernelShark's graphs.

Signed-off-by: Yordan Karadzhov (VMware) <y.karadz@gmail.com>
---
 kernel-shark-qt/src/CMakeLists.txt   |  13 ++
 kernel-shark-qt/src/libkshark-plot.c | 212 +++++++++++++++++++++++++++
 kernel-shark-qt/src/libkshark-plot.h |  69 +++++++++
 3 files changed, 294 insertions(+)
 create mode 100644 kernel-shark-qt/src/libkshark-plot.c
 create mode 100644 kernel-shark-qt/src/libkshark-plot.h

diff --git a/kernel-shark-qt/src/CMakeLists.txt b/kernel-shark-qt/src/CMakeLists.txt
index a762da1..9c74bc0 100644
--- a/kernel-shark-qt/src/CMakeLists.txt
+++ b/kernel-shark-qt/src/CMakeLists.txt
@@ -13,5 +13,18 @@ target_link_libraries(kshark ${CMAKE_DL_LIBS}
 
 set_target_properties(kshark  PROPERTIES SUFFIX	".so.${KS_VERSION_STRING}")
 
+if (OPENGL_FOUND AND GLUT_FOUND)
+
+    message(STATUS "libkshark-plot")
+    add_library(kshark-plot  SHARED  libkshark-plot.c)
+
+    target_link_libraries(kshark-plot  kshark
+                                       ${OPENGL_LIBRARIES}
+                                       ${GLUT_LIBRARY})
+
+    set_target_properties(kshark-plot PROPERTIES  SUFFIX ".so.${KS_VERSION_STRING}")
+
+endif (OPENGL_FOUND AND GLUT_FOUND)
+
 configure_file( ${KS_DIR}/build/deff.h.cmake
                 ${KS_DIR}/src/KsDeff.h)
diff --git a/kernel-shark-qt/src/libkshark-plot.c b/kernel-shark-qt/src/libkshark-plot.c
new file mode 100644
index 0000000..17d3b90
--- /dev/null
+++ b/kernel-shark-qt/src/libkshark-plot.c
@@ -0,0 +1,212 @@
+/* SPDX-License-Identifier: LGPL-2.1 */
+
+/*
+ * Copyright (C) 2018 VMware Inc, Yordan Karadzhov <y.karadz@gmail.com>
+ */
+
+ /**
+  *  @file    libkshark-plot.c
+  *  @brief   Basic tools for OpenGL plotting.
+  */
+
+// OpenGL
+#include <GL/freeglut.h>
+#include <GL/gl.h>
+
+// KernelShark
+#include "libkshark-plot.h"
+
+/**
+ * @brief Create an empty scene for drawing.
+ *
+ * @param width: Width of the screen window in pixels.
+ * @param height: Height of the screen window in pixels.
+ */
+void ksplot_make_scene(int width, int height)
+{
+	/* Set Display mode. */
+	glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
+
+	/* Prevent the program from exiting when a window is closed. */
+	glutSetOption(GLUT_ACTION_ON_WINDOW_CLOSE,
+		      GLUT_ACTION_GLUTMAINLOOP_RETURNS);
+
+	/* Set window size. */
+	glutInitWindowSize(width, height);
+
+	/* Set window position on screen. */
+	glutInitWindowPosition(50, 50);
+
+	/* Open the screen window. */
+	glutCreateWindow("KernelShark Plot");
+
+	/*
+	 * Set the origin of the coordinate system to be the top left corner.
+	 * The "Y" coordinate is inverted.
+	 */
+	gluOrtho2D(0, width, height, 0);
+	glViewport(0, 0, width, height);
+
+	glMatrixMode(GL_PROJECTION);
+	glLoadIdentity();
+}
+
+/**
+ * @brief Initialize OpenGL.
+ *
+ * @param dpr: Device Pixel Ratio.
+ */
+void ksplot_init_opengl(int dpr)
+{
+	glDisable(GL_TEXTURE_2D);
+	glDisable(GL_DEPTH_TEST);
+	glDisable(GL_COLOR_MATERIAL);
+	glEnable(GL_BLEND);
+	glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
+	glEnable(GL_POLYGON_SMOOTH);
+	glLineWidth(1.5 * dpr);
+	glPointSize(2.5 * dpr);
+	glClearColor(1, 1, 1, 1);
+}
+
+/**
+ * @brief To be called whenever the OpenGL window has been resized.
+ *
+ * @param width: Width of the screen window in pixels.
+ * @param height: Height of the screen window in pixels.
+ */
+void ksplot_resize_opengl(int width, int height)
+{
+	glViewport(0, 0, width, height);
+	glMatrixMode(GL_PROJECTION);
+	glLoadIdentity();
+
+	/*
+	 * Set the origin of the coordinate system to be the top left corner.
+	 * The "Y" coordinate is inverted.
+	 */
+	gluOrtho2D(0, width, height, 0);
+
+	glMatrixMode(GL_MODELVIEW);
+	glLoadIdentity();
+}
+
+/**
+ * @brief Draw a point.
+ *
+ * @param p: Input location for the point object.
+ * @param col: The color of the point.
+ * @param size: The size of the point.
+ */
+void ksplot_draw_point(const struct ksplot_point *p,
+		       const struct ksplot_color *col,
+		       float size)
+{
+	if (!p || !col || size < .5f)
+		return;
+
+	glPointSize(size);
+	glBegin(GL_POINTS);
+	glColor3ub(col->red, col->green, col->blue);
+	glVertex2i(p->x, p->y);
+	glEnd();
+}
+
+/**
+ * @brief Draw a line.
+ *
+ * @param a: Input location for the first finishing point of the line.
+ * @param b: Input location for the second finishing point of the line.
+ * @param col: The color of the line.
+ * @param size: The size of the line.
+ */
+void ksplot_draw_line(const struct ksplot_point *a,
+		      const struct ksplot_point *b,
+		      const struct ksplot_color *col,
+		      float size)
+{
+	if (!a || !b || !col || size < .5f)
+		return;
+
+	glLineWidth(size);
+	glBegin(GL_LINES);
+	glColor3ub(col->red, col->green, col->blue);
+	glVertex2i(a->x, a->y);
+	glVertex2i(b->x, b->y);
+	glEnd();
+}
+
+/**
+ * @brief Draw a polygon.
+ *
+ * @param points: Input location for the array of points defining the polygon.
+ * @param n_points: The size of the array of points.
+ * @param col: The color of the polygon.
+ * @param size: The size of the polygon.
+ */
+void ksplot_draw_polygon(const struct ksplot_point *points,
+			 size_t n_points,
+			 const struct ksplot_color *col,
+			 float size)
+{
+	if (!points || !n_points || !col || size < .5f)
+		return;
+
+	if (n_points == 1) {
+		ksplot_draw_point(points, col, size);
+		return;
+	}
+
+	if (n_points == 2) {
+		ksplot_draw_line(points, points + 1, col, size);
+		return;
+	}
+
+	/* Obtain a point inside the surface of the polygon. */
+	struct ksplot_point in_point;
+	in_point.x = (points[0].x + points[2].x) / 2;
+	in_point.y = (points[0].y + points[2].y) / 2;
+
+	/*
+	 * Draw a Triangle Fan using the internal point as a central
+	 * vertex.
+	 */
+	glBegin(GL_TRIANGLE_FAN);
+	glColor3ub(col->red, col->green, col->blue);
+	glVertex2i(in_point.x, in_point.y);
+	for (size_t i = 0; i < n_points; ++i)
+		glVertex2i(points[i].x, points[i].y);
+
+	glVertex2i(points[0].x, points[0].y);
+	glEnd();
+}
+
+/**
+ * @brief Draw the contour of a polygon.
+ *
+ * @param points: Input location for the array of points defining the polygon.
+ * @param n_points: The size of the array of points.
+ * @param col: The color of the polygon.
+ * @param size: The size of the polygon.
+ */
+void ksplot_draw_polygon_contour(const struct ksplot_point *points,
+				 size_t n_points,
+				 const struct ksplot_color *col,
+				 float size)
+{
+	if (!points || !n_points || !col || size < .5f)
+		return;
+
+	/* Loop over the points of the polygon and draw connecting lines. */
+	for(size_t i = 1; i < n_points; ++i)
+		ksplot_draw_line(&points[i - 1],
+				 &points[i],
+				 col,
+				 size);
+
+	/* Close the contour. */
+	ksplot_draw_line(&points[0],
+			 &points[n_points - 1],
+			 col,
+			 size);
+}
diff --git a/kernel-shark-qt/src/libkshark-plot.h b/kernel-shark-qt/src/libkshark-plot.h
new file mode 100644
index 0000000..9a4dbc0
--- /dev/null
+++ b/kernel-shark-qt/src/libkshark-plot.h
@@ -0,0 +1,69 @@
+/* SPDX-License-Identifier: LGPL-2.1 */
+
+/*
+ * Copyright (C) 2018 VMware Inc, Yordan Karadzhov <y.karadz@gmail.com>
+ */
+
+ /**
+  *  @file    libkshark-plot.h
+  *  @brief   Basic tools for OpenGL plotting.
+  */
+
+#ifndef _LIB_KSHARK_PLOT_H
+#define _LIB_KSHARK_PLOT_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/** Structure defining a RGB color. */
+struct ksplot_color {
+	/** The Red component of the color. */
+	uint8_t red;
+
+	/** The Green component of the color. */
+	uint8_t green;
+
+	/** The Blue component of the color. */
+	uint8_t blue;
+};
+
+/** Structure defining a 2D point. */
+struct ksplot_point {
+	/** The horizontal coordinate of the point in pixels. */
+	int x;
+
+	/** The vertical coordinate of the pointin in pixels. */
+	int y;
+};
+
+void ksplot_make_scene(int width, int height);
+
+void ksplot_init_opengl(int dpr);
+
+void ksplot_resize_opengl(int width, int height);
+
+void ksplot_draw_point(const struct ksplot_point *p,
+		       const struct ksplot_color *col,
+		       float size);
+
+void ksplot_draw_line(const struct ksplot_point *a,
+		      const struct ksplot_point *b,
+		      const struct ksplot_color *col,
+		      float size);
+
+void ksplot_draw_polygon(const struct ksplot_point *points,
+			 size_t n_points,
+			 const struct ksplot_color *col,
+			 float size);
+
+void ksplot_draw_polygon_contour(const struct ksplot_point *points,
+				 size_t n_points,
+				 const struct ksplot_color *col,
+				 float size);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif
-- 
2.17.1