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#include "OffscreenContext.h"
#include <GL/gl.h>
#include <GL/glu.h> // for gluCheckExtension
#include <SDL.h>
// Simple error reporting macros to help keep the sample code clean
#define REPORT_ERROR_AND_EXIT(desc) { std::cout << desc << "\n"; return false; }
#define NULL_ERROR_EXIT(test, desc) { if (!test) REPORT_ERROR_AND_EXIT(desc); }
struct OffscreenContext
{
int width;
int height;
GLuint fbo;
GLuint colorbo;
GLuint depthbo;
};
OffscreenContext *create_offscreen_context(int w, int h)
{
OffscreenContext *ctx = new OffscreenContext;
ctx->width = w;
ctx->height = h;
// dummy window
SDL_Init(SDL_INIT_VIDEO);
SDL_SetVideoMode(10,10,32,SDL_OPENGL);
/*
* Test if framebuffer objects are supported
*/
const GLubyte* strExt = glGetString(GL_EXTENSIONS);
GLboolean fboSupported = gluCheckExtension((const GLubyte*)"GL_EXT_framebuffer_object", strExt);
if (!fboSupported)
REPORT_ERROR_AND_EXIT("Your system does not support framebuffer extension - unable to render scene");
/*
* Create an FBO
*/
GLuint renderBuffer = 0;
GLuint depthBuffer = 0;
// Depth buffer to use for depth testing - optional if you're not using depth testing
glGenRenderbuffersEXT(1, &depthBuffer);
glBindRenderbufferEXT(GL_RENDERBUFFER_EXT, depthBuffer);
glRenderbufferStorageEXT(GL_RENDERBUFFER_EXT, GL_DEPTH_COMPONENT24, w, h);
REPORTGLERROR("creating depth render buffer");
// Render buffer to use for imaging
glGenRenderbuffersEXT(1, &renderBuffer);
glBindRenderbufferEXT(GL_RENDERBUFFER_EXT, renderBuffer);
glRenderbufferStorageEXT(GL_RENDERBUFFER_EXT, GL_RGBA8, w, h);
REPORTGLERROR("creating color render buffer");
ctx->fbo = 0;
glGenFramebuffersEXT(1, &ctx->fbo);
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, ctx->fbo);
REPORTGLERROR("binding framebuffer");
glFramebufferRenderbufferEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT,
GL_RENDERBUFFER_EXT, renderBuffer);
REPORTGLERROR("specifying color render buffer");
if (glCheckFramebufferStatusEXT(GL_FRAMEBUFFER_EXT) !=
GL_FRAMEBUFFER_COMPLETE_EXT)
REPORT_ERROR_AND_EXIT("Problem with OpenGL framebuffer after specifying color render buffer.");
glFramebufferRenderbufferEXT(GL_FRAMEBUFFER_EXT, GL_DEPTH_ATTACHMENT_EXT,
GL_RENDERBUFFER_EXT, depthBuffer);
REPORTGLERROR("specifying depth render buffer");
if (glCheckFramebufferStatusEXT(GL_FRAMEBUFFER_EXT) !=
GL_FRAMEBUFFER_COMPLETE_EXT)
REPORT_ERROR_AND_EXIT("Problem with OpenGL framebuffer after specifying depth render buffer.");
return ctx;
}
bool teardown_offscreen_context(OffscreenContext *ctx)
{
// "un"bind my FBO
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);
/*
* Cleanup
*/
return true;
}
void write_targa(const char *filename, GLubyte *pixels, int width, int height)
{
FILE *f = fopen( filename, "w" );
int y;
if (f) {
GLubyte header[] = {
00,00,02, 00,00,00, 00,00,00, 00,00,00,
0xff & width, 0xff & width >> 8,
0xff & height, 0xff & height >> 8,
32, 0x20 }; // next-to-last = bit depth
fwrite( header, sizeof(header), 1, f);
for (y=height-1; y>=0; y--)
fwrite( pixels + y*width*4, 4, width, f);
fclose(f);
}
}
bool save_framebuffer(OffscreenContext *ctx, const char *filename)
{
/*
* Extract the resulting rendering as an image
*/
int samplesPerPixel = 4; // R, G, B and A
GLubyte pixels[ ctx->width * ctx->height * samplesPerPixel ];
glReadPixels(0, 0, ctx->width, ctx->height, GL_BGRA, GL_UNSIGNED_BYTE, pixels);
printf("writing %s\n",filename);
write_targa(filename,pixels,ctx->width, ctx->height);
return true;
}
void bind_offscreen_context(OffscreenContext *ctx)
{
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, ctx->fbo);
}
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