1 //========================================================================
2 // Offscreen rendering example
3 // Copyright (c) Camilla Löwy <elmindreda@glfw.org>
4 //
5 // This software is provided 'as-is', without any express or implied
6 // warranty. In no event will the authors be held liable for any damages
7 // arising from the use of this software.
8 //
9 // Permission is granted to anyone to use this software for any purpose,
10 // including commercial applications, and to alter it and redistribute it
11 // freely, subject to the following restrictions:
12 //
13 // 1. The origin of this software must not be misrepresented; you must not
14 // claim that you wrote the original software. If you use this software
15 // in a product, an acknowledgment in the product documentation would
16 // be appreciated but is not required.
17 //
18 // 2. Altered source versions must be plainly marked as such, and must not
19 // be misrepresented as being the original software.
20 //
21 // 3. This notice may not be removed or altered from any source
22 // distribution.
23 //
24 //========================================================================
25
26 #define GLAD_GL_IMPLEMENTATION
27 #include <glad/gl.h>
28 #define GLFW_INCLUDE_NONE
29 #include <GLFW/glfw3.h>
30
31 #include "linmath.h"
32
33 #include <stdlib.h>
34 #include <stdio.h>
35
36 #define STB_IMAGE_WRITE_IMPLEMENTATION
37 #include <stb_image_write.h>
38
39 static const struct
40 {
41 float x, y;
42 float r, g, b;
43 } vertices[3] =
44 {
45 { -0.6f, -0.4f, 1.f, 0.f, 0.f },
46 { 0.6f, -0.4f, 0.f, 1.f, 0.f },
47 { 0.f, 0.6f, 0.f, 0.f, 1.f }
48 };
49
50 static const char* vertex_shader_text =
51 "#version 110\n"
52 "uniform mat4 MVP;\n"
53 "attribute vec3 vCol;\n"
54 "attribute vec2 vPos;\n"
55 "varying vec3 color;\n"
56 "void main()\n"
57 "{\n"
58 " gl_Position = MVP * vec4(vPos, 0.0, 1.0);\n"
59 " color = vCol;\n"
60 "}\n";
61
62 static const char* fragment_shader_text =
63 "#version 110\n"
64 "varying vec3 color;\n"
65 "void main()\n"
66 "{\n"
67 " gl_FragColor = vec4(color, 1.0);\n"
68 "}\n";
69
error_callback(int error,const char * description)70 static void error_callback(int error, const char* description)
71 {
72 fprintf(stderr, "Error: %s\n", description);
73 }
74
main(void)75 int main(void)
76 {
77 GLFWwindow* window;
78 GLuint vertex_buffer, vertex_shader, fragment_shader, program;
79 GLint mvp_location, vpos_location, vcol_location;
80 float ratio;
81 int width, height;
82 mat4x4 mvp;
83 char* buffer;
84
85 glfwSetErrorCallback(error_callback);
86
87 glfwInitHint(GLFW_COCOA_MENUBAR, GLFW_FALSE);
88
89 if (!glfwInit())
90 exit(EXIT_FAILURE);
91
92 glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 2);
93 glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 0);
94 glfwWindowHint(GLFW_VISIBLE, GLFW_FALSE);
95
96 window = glfwCreateWindow(640, 480, "Simple example", NULL, NULL);
97 if (!window)
98 {
99 glfwTerminate();
100 exit(EXIT_FAILURE);
101 }
102
103 glfwMakeContextCurrent(window);
104 gladLoadGL(glfwGetProcAddress);
105
106 // NOTE: OpenGL error checks have been omitted for brevity
107
108 glGenBuffers(1, &vertex_buffer);
109 glBindBuffer(GL_ARRAY_BUFFER, vertex_buffer);
110 glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
111
112 vertex_shader = glCreateShader(GL_VERTEX_SHADER);
113 glShaderSource(vertex_shader, 1, &vertex_shader_text, NULL);
114 glCompileShader(vertex_shader);
115
116 fragment_shader = glCreateShader(GL_FRAGMENT_SHADER);
117 glShaderSource(fragment_shader, 1, &fragment_shader_text, NULL);
118 glCompileShader(fragment_shader);
119
120 program = glCreateProgram();
121 glAttachShader(program, vertex_shader);
122 glAttachShader(program, fragment_shader);
123 glLinkProgram(program);
124
125 mvp_location = glGetUniformLocation(program, "MVP");
126 vpos_location = glGetAttribLocation(program, "vPos");
127 vcol_location = glGetAttribLocation(program, "vCol");
128
129 glEnableVertexAttribArray(vpos_location);
130 glVertexAttribPointer(vpos_location, 2, GL_FLOAT, GL_FALSE,
131 sizeof(vertices[0]), (void*) 0);
132 glEnableVertexAttribArray(vcol_location);
133 glVertexAttribPointer(vcol_location, 3, GL_FLOAT, GL_FALSE,
134 sizeof(vertices[0]), (void*) (sizeof(float) * 2));
135
136 glfwGetFramebufferSize(window, &width, &height);
137 ratio = width / (float) height;
138
139 glViewport(0, 0, width, height);
140 glClear(GL_COLOR_BUFFER_BIT);
141
142 mat4x4_ortho(mvp, -ratio, ratio, -1.f, 1.f, 1.f, -1.f);
143
144 glUseProgram(program);
145 glUniformMatrix4fv(mvp_location, 1, GL_FALSE, (const GLfloat*) mvp);
146 glDrawArrays(GL_TRIANGLES, 0, 3);
147 glFinish();
148
149 buffer = calloc(4, width * height);
150 glReadPixels(0, 0, width, height, GL_RGBA, GL_UNSIGNED_BYTE, buffer);
151
152 // Write image Y-flipped because OpenGL
153 stbi_write_png("offscreen.png",
154 width, height, 4,
155 buffer + (width * 4 * (height - 1)),
156 -width * 4);
157
158 free(buffer);
159
160 glfwDestroyWindow(window);
161
162 glfwTerminate();
163 exit(EXIT_SUCCESS);
164 }
165
166