openvr sdl opengl overlay example

overlay.cpp

// g++ overlay.cpp -o overlay $(pkg-config --cflags --libs gl sdl2) -lopenvr_api

#define GL_GLEXT_PROTOTYPES 1
#define GL3_PROTOTYPES 1
#include <GL/gl.h>

#include <iostream>
#include <SDL2/SDL.h>
#include <openvr/openvr.h>

using namespace vr;
void check_error(int line, EVRInitError error) { if (error != 0) printf("%d: error %s\n", line, VR_GetVRInitErrorAsSymbol(error)); }

int main(int argc, char **argv)
{
    float ppm = 64.;
    int width = 64;
	int height = 64;

    SDL_Window *window = SDL_CreateWindow("SDL2/OpenGL Demo", 0, 0, 640, 480, SDL_WINDOW_OPENGL|SDL_WINDOW_RESIZABLE);
    SDL_GLContext glcontext = SDL_GL_CreateContext(window);
    SDL_GL_SetSwapInterval(0);

    EVRInitError error;
    VR_Init(&error, vr::VRApplication_Overlay);
    check_error(__LINE__, error);

	uint8_t *gradientImage = (uint8_t*) malloc(sizeof(uint8_t) * width * height * 4);
    for (int i = 0; i < width * height; i++) {
        gradientImage[i * 4] = (float)i / width / width * 255.;
		gradientImage[i * 4 + 1] = 0;
		gradientImage[i * 4 + 2] = 0;
		gradientImage[i * 4 + 3] = 255;
    }
    GLuint texture;
    VROverlayHandle_t handle;

	char key[100];
	snprintf(key, 100, "testoverlay-%d", 1);
	VROverlay()->CreateOverlay (key, key, &handle);
	VROverlay()->SetOverlayWidthInMeters(handle, width / ppm);
	VROverlay()->ShowOverlay(handle);

	HmdMatrix34_t m = {0};
	m.m[0][0] = 1;
	m.m[1][1] = 1;
	m.m[2][2] = 1;

	m.m[0][3] = 0.; // x
	m.m[1][3] = 1.5; // y
	m.m[2][3] = -3.; // z
	VROverlay()->SetOverlayTransformAbsolute(handle, ETrackingUniverseOrigin::TrackingUniverseStanding, &m);

	glClearColor(0, 0, 0, 1);
	glClear(GL_COLOR_BUFFER_BIT);

	glGenTextures(1, &texture);
	glBindTexture(GL_TEXTURE_2D, texture);
	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, (GLvoid*)gradientImage);

	glFinish();
	Texture_t tex;
	tex.handle = (void*)(uintptr_t) texture;
	tex.eColorSpace = ColorSpace_Linear;
	tex.eType = TextureType_OpenGL;

	VROverlay()->SetOverlayTexture(handle, &tex);

	while (true) {
		SDL_GL_SwapWindow(window);
		SDL_Delay(1. / 60. * 1000.); // doesn't matter that it's not actually 60 fps
		SDL_Event event;
		while (SDL_PollEvent(&event)) {
			if (event.type == SDL_QUIT || (event.type == SDL_KEYDOWN && event.key.keysym.sym == SDLK_ESCAPE)) {
				goto quit;
			}
		}
	}

quit:
	VROverlay()->DestroyOverlay(handle);
	glDeleteTextures(1, &texture);

    SDL_Delay(100);
    free (gradientImage);
    SDL_GL_DeleteContext(glcontext);
}