Cairo version that actually works properly

blit_cairo.c

@@ -0,0 +1,262 @@
+#include <assert.h>
+#include <cairo-xcb.h>
+#include <cairo.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <time.h>
+#include <unistd.h>
+#include <xcb/xcb.h>
+
+void
+print_cairo_format(cairo_format_t format) {
+  switch (format) {
+    case CAIRO_FORMAT_INVALID:
+      printf("Invalid\n");
+      break;
+    case CAIRO_FORMAT_ARGB32:
+      printf("ARGB32\n");
+      break;
+    case CAIRO_FORMAT_RGB24:
+      printf("ARGB32\n");
+      break;
+    case CAIRO_FORMAT_A8:
+      printf("A8\n");
+      break;
+    case CAIRO_FORMAT_A1:
+      printf("A1\n");
+      break;
+    case CAIRO_FORMAT_RGB16_565:
+      printf("RGB16_565\n");
+      break;
+    case CAIRO_FORMAT_RGB30:
+      printf("RGB30\n");
+      break;
+    default:
+      break;
+  }
+}
+
+static xcb_visualtype_t*
+findVisual(xcb_connection_t *display,
+            xcb_visualid_t visual) {
+
+  /* Taken from here https://cairographics.org/cookbook/xcbsurface.c/ */
+  /* This function basically searches for a xcb_visualtype_t given a visual ID */
+
+  xcb_screen_iterator_t screen_iter = xcb_setup_roots_iterator(xcb_get_setup(display));
+
+  for(; screen_iter.rem; xcb_screen_next(&screen_iter)) {
+    /* Iterate over the screens available */
+
+    xcb_depth_iterator_t depth_iter = xcb_screen_allowed_depths_iterator(screen_iter.data);
+
+    for (; depth_iter.rem; xcb_depth_next(&depth_iter)) {
+      /* Iterate over the depths allowed on this screen */
+      xcb_visualtype_iterator_t visual_iter = xcb_depth_visuals_iterator(depth_iter.data);
+      /* depth_iter.data = the number of visuals available */
+
+      for (; visual_iter.rem; xcb_visualtype_next(&visual_iter)) {
+        /* Iterate over all of the visuals available */
+        if (visual == visual_iter.data->visual_id) {
+          printf("%u bits per rgb value\n", visual_iter.data->bits_per_rgb_value);
+          return visual_iter.data;
+        }
+      }
+    }
+  }
+  return NULL;
+}
+
+xcb_screen_t*
+allocScreen(xcb_connection_t *display) {
+  /* Gets a screen from the display connection */
+  const xcb_setup_t *setup = xcb_get_setup(display);
+  xcb_screen_iterator_t iter = xcb_setup_roots_iterator(setup);
+  xcb_screen_t *screen = iter.data;
+
+  return screen;
+}
+
+void
+swapBuffers(cairo_t *front_cr,
+            cairo_surface_t *backbuffer_surface,
+            unsigned char v,
+            int height) {
+
+  int stride = cairo_image_surface_get_stride(backbuffer_surface);
+
+  unsigned char *data = cairo_image_surface_get_data(backbuffer_surface);
+
+  memset(data, v, stride*height);
+
+  cairo_surface_flush(backbuffer_surface);
+
+  cairo_set_source_surface(front_cr,
+                           backbuffer_surface,
+                           0,
+                           0);
+
+  cairo_paint(front_cr);
+  cairo_surface_flush(backbuffer_surface);
+}
+
+cairo_surface_t*
+allocFrontBuf(xcb_connection_t *display,
+              xcb_drawable_t drawable,
+              xcb_screen_t *screen,
+              int width,
+              int height) {
+
+  cairo_surface_t *surface = cairo_xcb_surface_create(display,
+                                                      drawable,
+                                                      findVisual(display, screen->root_visual),
+                                                      width,
+                                                      height);
+
+  printf("Stride = %d\n", cairo_image_surface_get_stride(surface));
+
+  return surface;
+}
+
+cairo_surface_t*
+allocBackBuf(int width,
+             int height) {
+
+  cairo_format_t format = CAIRO_FORMAT_RGB24;
+
+  cairo_surface_t *surface = cairo_image_surface_create(format,
+                                                        width,
+                                                        height);
+
+  int stride = cairo_image_surface_get_stride(surface);
+
+  printf("Stride for image = %d\n", stride);
+
+  /* might not be needed */
+  cairo_surface_flush(surface);
+
+  return surface;
+}
+
+xcb_connection_t*
+allocDisplay() {
+  /* Get a display to use */
+  /* Currently just uses the default display */
+
+  xcb_connection_t *display = xcb_connect(NULL, NULL);
+
+  if (display == NULL) {
+    fprintf(stderr, "Could not open the display! :(\n");
+    exit(1);
+  }
+
+  return display;
+}
+
+xcb_window_t
+allocWindow(xcb_connection_t *display,
+            xcb_screen_t *screen,
+            uint16_t width,
+            uint16_t height) {
+  /* Create the window */
+  xcb_window_t window = xcb_generate_id(display);
+
+  xcb_cw_t mask = XCB_CW_BACK_PIXEL | XCB_CW_EVENT_MASK;
+
+  /* Define all the events we want to handle with xcb */
+  /* XCB_EVENT_MASK_EXPOSURE is the "exposure" event */
+  /* I.e. it fires when our window shows up on the screen */
+
+  uint32_t valwin[2] = {screen->white_pixel, XCB_EVENT_MASK_EXPOSURE};
+
+  xcb_create_window(display,
+                    XCB_COPY_FROM_PARENT,  /* depth (same as root) */
+                    window,
+                    screen->root, /* parent window */
+                    0, /* x */
+                    0, /* y */
+                    width,/* width */
+                    height,/* height */
+                    10, /* border_width  */
+                    XCB_WINDOW_CLASS_INPUT_OUTPUT, /* class */
+                    screen->root_visual, /* visual */
+                    mask, /* value mask, used for events */
+                    valwin); /* masks, used for events */
+
+  return window;
+}
+
+static struct timespec
+genSleep(time_t sec,
+         long nanosec) {
+  struct timespec t;
+  t.tv_sec = sec;
+  t.tv_nsec = nanosec;
+  return t;
+}
+
+int
+main (void) {
+
+  /* Used to handle the event loop */
+  struct timespec req = genSleep(0, 20000000);
+  struct timespec rem = genSleep(0, 0);
+
+  /* Open up the display */
+  xcb_connection_t *display = allocDisplay();
+
+  /* Get a handle to the screen */
+  xcb_screen_t *screen = allocScreen(display);
+
+  int window_height = screen->height_in_pixels;
+  int window_width = screen->width_in_pixels;
+
+  /* Create a window */
+  xcb_window_t window =
+    allocWindow(display,
+                screen,
+                window_width,
+                window_height);
+
+  /* Map the window to the display */
+  xcb_map_window(display, window);
+
+  /* Allocate front buffer (X drawable) */
+  cairo_surface_t *frontbuffer_surface =
+    allocFrontBuf(display,
+                  window,
+                  screen,
+                  window_width,
+                  window_height);
+
+  cairo_t *front_cr = cairo_create(frontbuffer_surface);
+
+  /* Allocate backbuffer (raw pixel buffer) */
+  cairo_surface_t *backbuffer_surface =
+    allocBackBuf(window_width, window_height);
+
+  cairo_t *back_cr = cairo_create(backbuffer_surface);
+
+  unsigned char v = 0;
+
+  while (1) {
+    swapBuffers(front_cr,
+                backbuffer_surface,
+                v,
+                window_height);
+    xcb_flush(display);
+    nanosleep(&req, &rem);
+    v++;
+  }
+
+  pause();
+
+  cairo_destroy(back_cr);
+  cairo_surface_destroy(backbuffer_surface);
+
+  cairo_destroy(front_cr);
+  cairo_surface_destroy(frontbuffer_surface);
+
+  return 0;
+}

blit_opengl.c

@@ -1,5 +1,6 @@
 #include <GL/gl.h>
 #include <GL/glx.h>
+#include <GL/glu.h>
 #include <X11/Xlib-xcb.h> /* for XGetXCBConnection, link with libX11-xcb */
 #include <X11/Xlib.h>
 #include <assert.h>
@@ -52,24 +53,18 @@ static int visual_attribs[] = {
  */
 #define RECEIVE_EVENT(ev) (ev->response_type & ~0x80)
 
-void draw(GLint offset) {
-  /* This is needed because now the contents of `drawable` are undefined */
-
-  printf("Drawing!\n");
-
-  glClearColor(0.0, 0.0, 0.0, 1.0);
-  glClear(GL_COLOR_BUFFER_BIT);
-
-  glMatrixMode(GL_PROJECTION);
-  glLoadIdentity();
-  glOrtho(0.0, 500, 500, 0.0, 0.0, 1.0);
-
-  glBegin(GL_POINTS);
-  for (int i = 0; i < 100; i++) {
-    glVertex2i(offset, i);
-  }
-  glEnd();
-
+void draw(uint16_t height,
+          uint16_t width) {
+   // Draw a Red 1x1 Square centered at origin
+   glBegin(GL_QUADS);              // Each set of 4 vertices form a quad
+      glColor3f(1.0f, 0.0f, 0.0f); // Red
+      glVertex2f(-0.5f, -0.5f);    // x, y
+      glVertex2f( 0.5f, -0.5f);
+      glVertex2f( 0.5f,  0.5f);
+      glVertex2f(-0.5f,  0.5f);
+   glEnd();
+ 
+   glFlush();  // Render now
 }
 
 static struct timespec
@@ -85,20 +80,30 @@ int
 message_loop(Display *display,
              xcb_connection_t *xcb_display,
              xcb_window_t window,
+             xcb_screen_t *screen,
              GLXDrawable drawable) {
 
     int running = 1;
 
-
     glClearColor(0.0, 0.0, 0.0, 1.0);
     glClear(GL_COLOR_BUFFER_BIT);
 
-    GLint offset = 0;
+    GLint x_offset = 0;
 
     /* Used to handle the event loop */
     struct timespec req = genSleep(0, 20000000);
     struct timespec rem = genSleep(0, 0);
 
+    xcb_expose_event_t *expose;
+
+    uint16_t window_height = screen->height_in_pixels;
+    uint16_t window_width = screen->width_in_pixels;
+
+    int exposed = 0;
+
+    glClearColor(0.0f, 0.0f, 0.0f, 1.0f); // Set background color to black and opaque
+    glClear(GL_COLOR_BUFFER_BIT);         // Clear the color buffer (background)
+
     while (running) {
         /* Poll for events */
 
@@ -111,7 +116,13 @@ message_loop(Display *display,
                 // running = 0;
                 break;
             case XCB_EXPOSE:
+                expose = (xcb_expose_event_t *)event;
+
+                window_height = expose->height;
+                window_width = expose->width;
+
                 printf("Got expose event\n");
+                exposed = 1;
                 break;
             default:
                 break;
@@ -119,28 +130,29 @@ message_loop(Display *display,
 
           free(event);
         }
-        draw(offset);
-        offset++;
-
-        /* This is where the magic happens */
-        /* This call will NOT block.*/
-        /* It will be sync'd with vertical refresh */
-        glXSwapBuffers(display, drawable);
-        nanosleep(&req, &rem);
-    }
 
+        if (exposed) {
+          draw(window_width, window_height);
+
+          /* This is where the magic happens */
+          /* This call will NOT block.*/
+          /* It will be sync'd with vertical refresh */
+          glXSwapBuffers(display, drawable);
+          nanosleep(&req, &rem);
+        }
+    }
     return 0;
 }
 
 int
 setup_message_loop(Display* display,
-              xcb_connection_t *xcb_display,
-              int default_screen,
-              xcb_screen_t *screen) {
+                   xcb_connection_t *xcb_display,
+                   int default_screen,
+                   xcb_screen_t *screen) {
 
     int visualID = 0;
-    uint16_t width = 500;
-    uint16_t height = 500;
+    uint16_t width = screen->width_in_pixels;
+    uint16_t height = screen->height_in_pixels;
 
     /* Query framebuffer configurations that match visual_attribs */
     GLXFBConfig *fb_configs = 0;
@@ -192,8 +204,7 @@ setup_message_loop(Display* display,
             display,
             fb_config,
             window,
-            0
-            );
+            0);
 
     if (!window) {
         xcb_destroy_window(xcb_display, window);
@@ -224,6 +235,7 @@ setup_message_loop(Display* display,
     int retval = message_loop(display,
                               xcb_display,
                               window,
+                              screen,
                               drawable);
 
     /* Cleanup */
@@ -383,7 +395,10 @@ main(void) {
     xcb_screen_t *screen = getScreen(xcb_display, default_screen);
 
     /* Initialize window and OpenGL context, run main loop and deinitialize */
-    int retval = setup_message_loop(display, xcb_display, default_screen, screen);
+    int retval = setup_message_loop(display,
+                                    xcb_display,
+                                    default_screen,
+                                    screen);
 
     /* Cleanup */
     XCloseDisplay(display);