Add offscreen rendering example

examples/CMakeLists.txt

@@ -11,6 +11,10 @@ if (MSVC)
     add_definitions(-D_CRT_SECURE_NO_WARNINGS)
 endif()
 
+if (GLFW_USE_OSMESA)
+    add_definitions(-DUSE_NATIVE_OSMESA)
+endif()
+
 include_directories("${GLFW_SOURCE_DIR}/deps")
 
 if (WIN32)
@@ -31,6 +35,7 @@ set(TINYCTHREAD "${GLFW_SOURCE_DIR}/deps/tinycthread.h"
 add_executable(boing WIN32 MACOSX_BUNDLE boing.c ${ICON} ${GLAD})
 add_executable(gears WIN32 MACOSX_BUNDLE gears.c ${ICON} ${GLAD})
 add_executable(heightmap WIN32 MACOSX_BUNDLE heightmap.c ${ICON} ${GLAD})
+add_executable(offscreen offscreen.c ${ICON} ${GLAD})
 add_executable(particles WIN32 MACOSX_BUNDLE particles.c ${ICON} ${TINYCTHREAD} ${GETOPT} ${GLAD})
 add_executable(simple WIN32 MACOSX_BUNDLE simple.c ${ICON} ${GLAD})
 add_executable(splitview WIN32 MACOSX_BUNDLE splitview.c ${ICON} ${GLAD})

examples/offscreen.c

@@ -0,0 +1,171 @@
+//========================================================================
+// Offscreen rendering example
+// Copyright (c) Camilla Berglund <elmindreda@glfw.org>
+//
+// This software is provided 'as-is', without any express or implied
+// warranty. In no event will the authors be held liable for any damages
+// arising from the use of this software.
+//
+// Permission is granted to anyone to use this software for any purpose,
+// including commercial applications, and to alter it and redistribute it
+// freely, subject to the following restrictions:
+//
+// 1. The origin of this software must not be misrepresented; you must not
+//    claim that you wrote the original software. If you use this software
+//    in a product, an acknowledgment in the product documentation would
+//    be appreciated but is not required.
+//
+// 2. Altered source versions must be plainly marked as such, and must not
+//    be misrepresented as being the original software.
+//
+// 3. This notice may not be removed or altered from any source
+//    distribution.
+//
+//========================================================================
+
+#include <glad/glad.h>
+#include <GLFW/glfw3.h>
+
+#if USE_NATIVE_OSMESA
+ #define GLFW_EXPOSE_NATIVE_OSMESA
+ #include <GLFW/glfw3native.h>
+#endif
+
+#include "linmath.h"
+
+#include <stdlib.h>
+#include <stdio.h>
+
+#define STB_IMAGE_WRITE_IMPLEMENTATION
+#include <stb_image_write.h>
+
+static const struct
+{
+    float x, y;
+    float r, g, b;
+} vertices[3] =
+{
+    { -0.6f, -0.4f, 1.f, 0.f, 0.f },
+    {  0.6f, -0.4f, 0.f, 1.f, 0.f },
+    {   0.f,  0.6f, 0.f, 0.f, 1.f }
+};
+
+static const char* vertex_shader_text =
+"uniform mat4 MVP;\n"
+"attribute vec3 vCol;\n"
+"attribute vec2 vPos;\n"
+"varying vec3 color;\n"
+"void main()\n"
+"{\n"
+"    gl_Position = MVP * vec4(vPos, 0.0, 1.0);\n"
+"    color = vCol;\n"
+"}\n";
+
+static const char* fragment_shader_text =
+"varying vec3 color;\n"
+"void main()\n"
+"{\n"
+"    gl_FragColor = vec4(color, 1.0);\n"
+"}\n";
+
+static void error_callback(int error, const char* description)
+{
+    fprintf(stderr, "Error: %s\n", description);
+}
+
+int main(void)
+{
+    GLFWwindow* window;
+    GLuint vertex_buffer, vertex_shader, fragment_shader, program;
+    GLint mvp_location, vpos_location, vcol_location;
+    float ratio;
+    int width, height;
+    mat4x4 mvp;
+    char* buffer;
+
+    glfwSetErrorCallback(error_callback);
+
+    if (!glfwInit())
+        exit(EXIT_FAILURE);
+
+    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 2);
+    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 0);
+    glfwWindowHint(GLFW_VISIBLE, GLFW_FALSE);
+
+    window = glfwCreateWindow(640, 480, "Simple example", NULL, NULL);
+    if (!window)
+    {
+        glfwTerminate();
+        exit(EXIT_FAILURE);
+    }
+
+    glfwMakeContextCurrent(window);
+    gladLoadGLLoader((GLADloadproc) glfwGetProcAddress);
+
+    // NOTE: OpenGL error checks have been omitted for brevity
+
+    glGenBuffers(1, &vertex_buffer);
+    glBindBuffer(GL_ARRAY_BUFFER, vertex_buffer);
+    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
+
+    vertex_shader = glCreateShader(GL_VERTEX_SHADER);
+    glShaderSource(vertex_shader, 1, &vertex_shader_text, NULL);
+    glCompileShader(vertex_shader);
+
+    fragment_shader = glCreateShader(GL_FRAGMENT_SHADER);
+    glShaderSource(fragment_shader, 1, &fragment_shader_text, NULL);
+    glCompileShader(fragment_shader);
+
+    program = glCreateProgram();
+    glAttachShader(program, vertex_shader);
+    glAttachShader(program, fragment_shader);
+    glLinkProgram(program);
+
+    mvp_location = glGetUniformLocation(program, "MVP");
+    vpos_location = glGetAttribLocation(program, "vPos");
+    vcol_location = glGetAttribLocation(program, "vCol");
+
+    glEnableVertexAttribArray(vpos_location);
+    glVertexAttribPointer(vpos_location, 2, GL_FLOAT, GL_FALSE,
+                          sizeof(vertices[0]), (void*) 0);
+    glEnableVertexAttribArray(vcol_location);
+    glVertexAttribPointer(vcol_location, 3, GL_FLOAT, GL_FALSE,
+                          sizeof(vertices[0]), (void*) (sizeof(float) * 2));
+
+    glfwGetFramebufferSize(window, &width, &height);
+    ratio = width / (float) height;
+
+    glViewport(0, 0, width, height);
+    glClear(GL_COLOR_BUFFER_BIT);
+
+    mat4x4_ortho(mvp, -ratio, ratio, -1.f, 1.f, 1.f, -1.f);
+
+    glUseProgram(program);
+    glUniformMatrix4fv(mvp_location, 1, GL_FALSE, (const GLfloat*) mvp);
+    glDrawArrays(GL_TRIANGLES, 0, 3);
+
+#if USE_NATIVE_OSMESA
+    glfwGetOSMesaColorBuffer(window, &width, &height, NULL, (void**) &buffer);
+#else
+    buffer = calloc(4, width * height);
+    glReadPixels(0, 0, width, height, GL_RGBA, GL_UNSIGNED_BYTE, buffer);
+#endif
+
+    // Write image Y-flipped because OpenGL
+    stbi_write_png("offscreen.png",
+                   width, height, 4,
+                   buffer + (width * 4 * (height - 1)),
+                   -width * 4);
+
+#if USE_NATIVE_OSMESA
+    // Here is where there's nothing
+#else
+    free(buffer);
+#endif
+
+    glfwDestroyWindow(window);
+
+    glfwTerminate();
+    exit(EXIT_SUCCESS);
+}
+