// gcc -std=c99 makecurrent.c -o makecurrent -lGL -lGLU -lglut -lm -W -Wall -Wextra -ggdb

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <assert.h>

#define GL_GLEXT_PROTOTYPES
#include <GL/gl.h>
#include <GL/glext.h>
#include <GL/glut.h>
#include <GL/glx.h>

static int width = 800;
static int height = 400;

GLuint tex0;
GLuint tex1;

GLboolean enableMakeCurrent = GL_TRUE;

int pbuffer;

static void initTextures(void)
{
    float scratch[32*32*3], *ptr;

    // tex0: chessboard
    ptr = scratch;
    for (int i=0; i<32; ++i) {
        for (int j=0; j<32; ++j) {
            int ii = (i>>1)&1;
            int jj = (j>>1)&1;
            float val = ii==jj ? 1.0f : 0.0f;
            ptr[0] = val;
            ptr[1] = val;
            ptr[2] = val;
            ptr += 3;
        }
    }
    glGenTextures(1, &tex0);
    glBindTexture(GL_TEXTURE_2D, tex0);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, 32, 32, 0, GL_RGB, GL_FLOAT, (void*)scratch);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER,GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER,GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);

    // tex1: rainbow
    ptr = scratch;
    for (int i=0; i<32; ++i) {
        for (int j=0; j<32; ++j) {
            ptr[0] = 1.0f*i/32.0f;
            ptr[1] = 1.0f*j/32.0f;
            ptr[2] = (32-i-j)/32.0f;
            ptr += 3;
        }
    }
    glGenTextures(1, &tex1);
    glBindTexture(GL_TEXTURE_2D, tex1);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, 32, 32, 0, GL_RGB, GL_FLOAT, (void*)scratch);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER,GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER,GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
}

static void display(void)
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glActiveTextureARB(GL_TEXTURE0);
    glEnable(GL_TEXTURE_2D);
    glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE);

    glBindTexture(GL_TEXTURE_2D, tex0);
    glBegin(GL_QUADS);
    glMultiTexCoord2f(GL_TEXTURE0, 0.0, 0.0);
    glVertex3f(0.0, 0.0, -0.0);
    glMultiTexCoord2f(GL_TEXTURE0, 1.0, 0.0);
    glVertex3f(1.0, 0.0, -0.5);
    glMultiTexCoord2f(GL_TEXTURE0, 1.0, 1.0);
    glVertex3f(1.0, 1.0, -1.0);
    glMultiTexCoord2f(GL_TEXTURE0, 0.0, 1.0);
    glVertex3f(0.0, 1.0, -0.5);
    glEnd();

    if (enableMakeCurrent) {
        Display *dpy = glXGetCurrentDisplay();
        int current_drawable = glXGetCurrentDrawable();
        GLXContext context = glXGetCurrentContext();
        glXMakeCurrent(dpy, pbuffer, context); // Issue #1: Mesa warning: MakeCurrent: incompatible visuals for context and drawbuffer (pbuffer has no depth or stencil)
        glColor3f(1.0f, 0.0f, 1.0f); // this is no-op because of the above
        glXMakeCurrent(dpy, current_drawable, context);
        // Issue #2: depth buffer is now lost (so is stencil), subsequent rendering fails depth test
        //      because the newly allocated depth buffer is all zeros
        //      (with DRI3 the already drawn image is partially overwritten with noise, DRI2 only looses the non-color buffers)
    }

    glBindTexture(GL_TEXTURE_2D, tex1);
    glBegin(GL_QUADS);
    glMultiTexCoord2f(GL_TEXTURE0, 0.0, 0.0);
    glVertex3f(0.0, 0.0, -1.0);
    glMultiTexCoord2f(GL_TEXTURE0, 1.0, 0.0);
    glVertex3f(1.0, 0.0, -0.5);
    glMultiTexCoord2f(GL_TEXTURE0, 1.0, 1.0);
    glVertex3f(1.0, 1.0, -0.0);
    glMultiTexCoord2f(GL_TEXTURE0, 0.0, 1.0);
    glVertex3f(0.0, 1.0, -0.5);
    glEnd();

    glutSwapBuffers();
}

static void reshape(int w, int h)
{
    glViewport (0, 0, (GLsizei) w, (GLsizei) h);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(0.0, 1.0, 0.0, 1.0, 0.0, 1.0);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
}

static void keyboard(unsigned char key, int x, int y)
{
    (void)x;
    (void)y;
    if (key == ' ') {
        enableMakeCurrent = !enableMakeCurrent;
        printf("MakeCurrent is now %sabled\n", enableMakeCurrent?"en":"dis");
        glutPostRedisplay();
    } else if (key == 'q' || key == 27 /* ESC */) {
        exit(0);
    }
}

static const int attrib_list[] = {
    GLX_RED_SIZE, 8,
    GLX_GREEN_SIZE, 8,
    GLX_BLUE_SIZE, 8,
    GLX_ALPHA_SIZE, 8,
    /*GLX_DEPTH_SIZE, 24,
    GLX_STENCIL_SIZE, 8,*/
    GLX_DOUBLEBUFFER, GL_FALSE,
    GLX_DRAWABLE_TYPE, GLX_PBUFFER_BIT,
    GLX_RENDER_TYPE, GLX_RGBA_BIT,
    0};

static const int fb_size[] = {
    GLX_PBUFFER_WIDTH, 512,
    GLX_PBUFFER_HEIGHT, 512,
    0};

static void init(void)
{
    glColor3f(0.0f, 1.0f, 0.0f);
    glEnable(GL_DEPTH_TEST);

    initTextures();

    Display *dpy = glXGetCurrentDisplay();

    int nelements = 0;
    GLXFBConfig *configs = glXChooseFBConfig(dpy, 0, attrib_list, &nelements);
    printf("got %d configs\n", nelements);
    for (int i=0; i<nelements; i++) {
        int xid = 0;
        int attr = 0;
        if (glXGetFBConfigAttrib(dpy, configs[i], GLX_FBCONFIG_ID, &xid))
            assert(!"Can't get fbconfig xid");
        if (glXGetFBConfigAttrib(dpy, configs[i], GLX_DEPTH_SIZE, &attr))
            assert(!"Can't get fbconfig attr");

        printf("xid %#x attr %d\n", xid, attr);
    }
    pbuffer = glXCreatePbuffer(dpy, configs[0], fb_size);
    assert(pbuffer);
}


static void fini(void)
{
}

int main(int argc, char **argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE | GLUT_DEPTH | GLUT_STENCIL);
    glutInitWindowSize(width, height);
    glutCreateWindow("Test program for glXMakeCurrent()");

    glutDisplayFunc(display);
    glutReshapeFunc(reshape);
    glutKeyboardFunc(keyboard);
    glutIdleFunc(glutPostRedisplay);

    init();

    glutMainLoop();

    fini();
}