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Cogl on BeagleBone

Clutter relies on Cogl as a backend for drawing geometric shapes. There aren't that many updated examples of using Python as a language binding for Cogl, but there are some Vala examples.

Here is the well known crate example. This should compile fine in BeagleBone using the Cogl packages from the Thing feed. The path to the crate.jpg file has been hard coded, so that needs to be changed.

#define COGL_ENABLE_EXPERIMENTAL_2_0_API

#include <cogl/cogl.h>
#include <cogl-pango/cogl-pango.h>

/* The state for this example... */
typedef struct _Data
{
  CoglFramebuffer *fb;
  int framebuffer_width;
  int framebuffer_height;

  CoglMatrix view;

  CoglIndices *indices;
  CoglPrimitive *prim;
  CoglTexture *texture;
  CoglPipeline *crate_pipeline;

  CoglPangoFontMap *pango_font_map;
  PangoContext *pango_context;
  PangoFontDescription *pango_font_desc;

  PangoLayout *hello_label;
  int hello_label_width;
  int hello_label_height;

  GTimer *timer;

  CoglBool swap_ready;

} Data;

/* A static identity matrix initialized for convenience. */
static CoglMatrix identity;
/* static colors initialized for convenience. */
static CoglColor white;

/* A cube modelled using 4 vertices for each face.
 *
 * We use an index buffer when drawing the cube later so the GPU will
 * actually read each face as 2 separate triangles.
 */
static CoglVertexP3T2 vertices[] =
{
  /* Front face */
  { /* pos = */ -1.0f, -1.0f,  1.0f, /* tex coords = */ 0.0f, 1.0f},
  { /* pos = */  1.0f, -1.0f,  1.0f, /* tex coords = */ 1.0f, 1.0f},
  { /* pos = */  1.0f,  1.0f,  1.0f, /* tex coords = */ 1.0f, 0.0f},
  { /* pos = */ -1.0f,  1.0f,  1.0f, /* tex coords = */ 0.0f, 0.0f},

  /* Back face */
  { /* pos = */ -1.0f, -1.0f, -1.0f, /* tex coords = */ 1.0f, 0.0f},
  { /* pos = */ -1.0f,  1.0f, -1.0f, /* tex coords = */ 1.0f, 1.0f},
  { /* pos = */  1.0f,  1.0f, -1.0f, /* tex coords = */ 0.0f, 1.0f},
  { /* pos = */  1.0f, -1.0f, -1.0f, /* tex coords = */ 0.0f, 0.0f},

  /* Top face */
  { /* pos = */ -1.0f,  1.0f, -1.0f, /* tex coords = */ 0.0f, 1.0f},
  { /* pos = */ -1.0f,  1.0f,  1.0f, /* tex coords = */ 0.0f, 0.0f},
  { /* pos = */  1.0f,  1.0f,  1.0f, /* tex coords = */ 1.0f, 0.0f},
  { /* pos = */  1.0f,  1.0f, -1.0f, /* tex coords = */ 1.0f, 1.0f},

  /* Bottom face */
  { /* pos = */ -1.0f, -1.0f, -1.0f, /* tex coords = */ 1.0f, 1.0f},
  { /* pos = */  1.0f, -1.0f, -1.0f, /* tex coords = */ 0.0f, 1.0f},
  { /* pos = */  1.0f, -1.0f,  1.0f, /* tex coords = */ 0.0f, 0.0f},
  { /* pos = */ -1.0f, -1.0f,  1.0f, /* tex coords = */ 1.0f, 0.0f},

  /* Right face */
  { /* pos = */ 1.0f, -1.0f, -1.0f, /* tex coords = */ 1.0f, 0.0f},
  { /* pos = */ 1.0f,  1.0f, -1.0f, /* tex coords = */ 1.0f, 1.0f},
  { /* pos = */ 1.0f,  1.0f,  1.0f, /* tex coords = */ 0.0f, 1.0f},
  { /* pos = */ 1.0f, -1.0f,  1.0f, /* tex coords = */ 0.0f, 0.0f},

  /* Left face */
  { /* pos = */ -1.0f, -1.0f, -1.0f, /* tex coords = */ 0.0f, 0.0f},
  { /* pos = */ -1.0f, -1.0f,  1.0f, /* tex coords = */ 1.0f, 0.0f},
  { /* pos = */ -1.0f,  1.0f,  1.0f, /* tex coords = */ 1.0f, 1.0f},
  { /* pos = */ -1.0f,  1.0f, -1.0f, /* tex coords = */ 0.0f, 1.0f}
};

static void
paint (Data *data)
{
  CoglFramebuffer *fb = data->fb;
  float rotation;

  cogl_framebuffer_clear4f (fb,
                            COGL_BUFFER_BIT_COLOR|COGL_BUFFER_BIT_DEPTH,
                            0, 0, 0, 1);

  cogl_framebuffer_push_matrix (fb);

  cogl_framebuffer_translate (fb,
                              data->framebuffer_width / 2,
                              data->framebuffer_height / 2,
                              0);

  cogl_framebuffer_scale (fb, 75, 75, 75);

  /* Update the rotation based on the time the application has been
     running so that we get a linear animation regardless of the frame
     rate */
  rotation = g_timer_elapsed (data->timer, NULL) * 60.0f;

  /* Rotate the cube separately around each axis.
   *
   * Note: Cogl matrix manipulation follows the same rules as for
   * OpenGL. We use column-major matrices and - if you consider the
   * transformations happening to the model - then they are combined
   * in reverse order which is why the rotation is done last, since
   * we want it to be a rotation around the origin, before it is
   * scaled and translated.
   */
  cogl_framebuffer_rotate (fb, rotation, 0, 0, 1);
  cogl_framebuffer_rotate (fb, rotation, 0, 1, 0);
  cogl_framebuffer_rotate (fb, rotation, 1, 0, 0);

  cogl_primitive_draw (data->prim, fb, data->crate_pipeline);

  cogl_framebuffer_pop_matrix (fb);
}

static void
frame_event_cb (CoglOnscreen *onscreen,
                CoglFrameEvent event,
                CoglFrameInfo *info,
                void *user_data)
{
  Data *data = user_data;

  if (event == COGL_FRAME_EVENT_SYNC)
    data->swap_ready = TRUE;
}

int
main (int argc, char **argv)
{
  CoglContext *ctx;
  CoglOnscreen *onscreen;
  CoglFramebuffer *fb;
  CoglError *error = NULL;
  Data data;
  PangoRectangle hello_label_size;
  float fovy, aspect, z_near, z_2d, z_far;
  CoglDepthState depth_state;

  ctx = cogl_context_new (NULL, &error);
  if (!ctx) {
      fprintf (stderr, "Failed to create context: %s\n", error->message);
      return 1;
  }

  onscreen = cogl_onscreen_new (ctx, 640, 480);
  fb = onscreen;
  data.fb = fb;
  data.framebuffer_width = cogl_framebuffer_get_width (fb);
  data.framebuffer_height = cogl_framebuffer_get_height (fb);

  data.timer = g_timer_new ();

  cogl_onscreen_show (onscreen);

  cogl_framebuffer_set_viewport (fb,
                                 0, 0,
                                 data.framebuffer_width,
                                 data.framebuffer_height);

  fovy = 60; /* y-axis field of view */
  aspect = (float)data.framebuffer_width/(float)data.framebuffer_height;
  z_near = 0.1; /* distance to near clipping plane */
  z_2d = 1000; /* position to 2d plane */
  z_far = 2000; /* distance to far clipping plane */

  cogl_framebuffer_perspective (fb, fovy, aspect, z_near, z_far);

  /* Since the pango renderer emits geometry in pixel/device coordinates
   * and the anti aliasing is implemented with the assumption that the
   * geometry *really* does end up pixel aligned, we setup a modelview
   * matrix so that for geometry in the plane z = 0 we exactly map x
   * coordinates in the range [0,stage_width] and y coordinates in the
   * range [0,stage_height] to the framebuffer extents with (0,0) being
   * the top left.
   *
   * This is roughly what Clutter does for a ClutterStage, but this
   * demonstrates how it is done manually using Cogl.
   */
  cogl_matrix_init_identity (&data.view);
  cogl_matrix_view_2d_in_perspective (&data.view, fovy, aspect, z_near, z_2d,
                                      data.framebuffer_width,
                                      data.framebuffer_height);
  cogl_framebuffer_set_modelview_matrix (fb, &data.view);

  /* Initialize some convenient constants */
  cogl_matrix_init_identity (&identity);
  cogl_color_init_from_4ub (&white, 0xff, 0xff, 0xff, 0xff);

  /* rectangle indices allow the GPU to interpret a list of quads (the
   * faces of our cube) as a list of triangles.
   *
   * Since this is a very common thing to do
   * cogl_get_rectangle_indices() is a convenience function for
   * accessing internal index buffers that can be shared.
   */
  data.indices = cogl_get_rectangle_indices (ctx, 6 /* n_rectangles */);
  data.prim = cogl_primitive_new_p3t2 (ctx, COGL_VERTICES_MODE_TRIANGLES,
                                       G_N_ELEMENTS (vertices),
                                       vertices);
  /* Each face will have 6 indices so we have 6 * 6 indices in total... */
  cogl_primitive_set_indices (data.prim,
                              data.indices,
                              6 * 6);

  /* Load a jpeg crate texture from a file */
  printf ("crate.jpg (CC by-nc-nd http://bit.ly/9kP45T) ShadowRunner27 http://bit.ly/m1YXLh\n");
  data.texture =
    cogl_texture_2d_new_from_file (ctx,
                                   "/usr/src/snuff/crate.jpg",
                                   COGL_PIXEL_FORMAT_ANY,
                                   &error);
  fprintf(stderr, "texture ok\n");

  if (!data.texture)
    g_error ("Failed to load texture: %s", error->message);

  /* a CoglPipeline conceptually describes all the state for vertex
   * processing, fragment processing and blending geometry. When
   * drawing the geometry for the crate this pipeline says to sample a
   * single texture during fragment processing... */
  data.crate_pipeline = cogl_pipeline_new (ctx);
  cogl_pipeline_set_layer_texture (data.crate_pipeline, 0, data.texture);
  /* Since the box is made of multiple triangles that will overlap
   * when drawn and we don't control the order they are drawn in, we
   * enable depth testing to make sure that triangles that shouldn't
   * be visible get culled by the GPU. */
  cogl_depth_state_init (&depth_state);
  cogl_depth_state_set_test_enabled (&depth_state, TRUE);
  cogl_pipeline_set_depth_state (data.crate_pipeline, &depth_state, NULL);
  /* Setup a Pango font map and context */


  data.swap_ready = TRUE;

  cogl_onscreen_add_frame_callback (COGL_ONSCREEN (fb),
                                    frame_event_cb,
                                    &data,
                                    NULL); /* destroy notify */


  while (1)
    {
      CoglPollFD *poll_fds;
      int n_poll_fds;
      int64_t timeout;

      if (data.swap_ready)
        {
          paint (&data);
          cogl_onscreen_swap_buffers (COGL_ONSCREEN (fb));
        }

      cogl_poll_renderer_get_info (cogl_context_get_renderer (ctx),
                                   &poll_fds, &n_poll_fds, &timeout);

      g_poll ((GPollFD *) poll_fds, n_poll_fds,
              timeout == -1 ? -1 : timeout / 1000);

      cogl_poll_renderer_dispatch (cogl_context_get_renderer (ctx),
                                   poll_fds, n_poll_fds);
    }

  return 0;
}

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