+/* gltest - small OpenGL tearing test program
+ * Copyright (C) 2012-2013 Ralf Jung <post@ralfj.de>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include "glutil.h"
+
+// shaders
+static const char *vertex_shader_source =
+"#version 100 \n\
+attribute vec2 position; \n\
+attribute vec3 color; \n\
+varying vec3 frag_color; \n\
+void main() \n\
+{ \n\
+ frag_color = color; \n\
+ gl_Position = vec4(position * vec2(2) - vec2(1), 0.0, 1.0); \n\
+}";
+static const char *fragment_shader_source =
+"#version 100 \n\
+varying vec3 frag_color; \n\
+void main(void) \n\
+{ \n\
+ gl_FragColor = vec4(frag_color, 1.0); \n\
+}";
+
+
+// OpenGL IDs (yeah, this is a bad hack... do we care?)
+static GLuint program;
+static struct {
+ GLint position;
+ GLint color;
+} attributes;
+
+// some local hlper functions
+static void show_info_log(GLuint object)
+{
+ GLint log_length;
+ glGetShaderiv(object, GL_INFO_LOG_LENGTH, &log_length);
+ char *log = new char[log_length];
+ glGetShaderInfoLog(object, log_length, NULL, log);
+ fprintf(stderr, "%s", log);
+ delete[] log;
+}
+
+static GLuint compile_shader(GLenum shader_type, const char *source)
+{
+ GLuint shader = glCreateShader(shader_type);
+ glShaderSource(shader, 1, &source, NULL);
+ glCompileShader(shader);
+ GLint shader_ok;
+ glGetShaderiv(shader, GL_COMPILE_STATUS, &shader_ok);
+ if (!shader_ok) {
+ fprintf(stderr, "Failed to compile shader\n");
+ show_info_log(shader);
+ exit(1);
+ }
+ return shader;
+}
+
+static GLuint createArrayBuffer(GLsizeiptr size, GLfloat *data)
+{
+ GLuint buffer;
+ glGenBuffers(1, &buffer);
+ glBindBuffer(GL_ARRAY_BUFFER, buffer);
+ glBufferData(GL_ARRAY_BUFFER, size, data, GL_STATIC_DRAW);
+ return buffer;
+}
+
+// initialisation
+void initialise2dProjection()
+{
+ GLuint vertex_shader = compile_shader(GL_VERTEX_SHADER, vertex_shader_source);
+ GLuint fragment_shader = compile_shader(GL_FRAGMENT_SHADER, fragment_shader_source);
+ program = glCreateProgram();
+ glAttachShader(program, vertex_shader);
+ glAttachShader(program, fragment_shader);
+ glLinkProgram(program);
+ attributes.position = glGetAttribLocation(program, "position");
+ attributes.color = glGetAttribLocation(program, "color");
+}
+
+// draw a quad
+void drawQuad(GLfloat red, GLfloat green, GLfloat blue, GLfloat x1, GLfloat y1, GLfloat x2, GLfloat y2)
+{
+ glUseProgram(program);
+
+ // send vertex data to card with given attribute
+ GLfloat vertex_buffer_data[] = {
+ x1, y1,
+ x2, y1,
+ x2, y2,
+ x1, y2,
+ };
+ GLuint vertex_buffer = createArrayBuffer(sizeof(vertex_buffer_data), vertex_buffer_data);
+ glVertexAttribPointer(
+ attributes.position, /* attribute */
+ 2, /* size */
+ GL_FLOAT, /* type */
+ GL_FALSE, /* normalized? */
+ 0, /* stride */
+ (void*)0 /* array buffer offset */
+ );
+ glEnableVertexAttribArray(attributes.position);
+
+ // same with color data
+ GLfloat color_buffer_data[] = {
+ red, green, blue,
+ red, green, blue,
+ red, green, blue,
+ red, green, blue,
+ };
+ GLuint color_buffer = createArrayBuffer(sizeof(color_buffer_data), color_buffer_data);
+ glVertexAttribPointer(
+ attributes.color, /* attribute */
+ 3, /* size */
+ GL_FLOAT, /* type */
+ GL_FALSE, /* normalized? */
+ 0, /* stride */
+ (void*)0 /* array buffer offset */
+ );
+ glEnableVertexAttribArray(attributes.color);
+
+ // draw
+ glDrawArrays(GL_TRIANGLE_FAN, 0, 4);
+
+ // cleanup
+ glDeleteBuffers(1, &vertex_buffer);
+ glDeleteBuffers(1, &color_buffer);
+}
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