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diff --git a/posts/pangocairo.md b/posts/pangocairo.md deleted file mode 100644 index fd651b5..0000000 --- a/posts/pangocairo.md +++ /dev/null @@ -1,321 +0,0 @@ -title: Font Rendering in OpenGL with Pango and Cairo -date: 2013-08-17 16:00:00 -tags: opengl, pango, cairo, font, wsu -summary: A brief tutorial for rendering fonts in OpenGL with libpangocairo ---- - -I am working towards a 0.1 release of my game development framework -for GNU Guile, [guile-2d](https://github.com/davexunit/guile-2d). One -of the few remaining blockers on my to-do list is font rendering. A -reddit user, [Madsy9](http://www.reddit.com/user/Madsy9), pointed me -in the right direction with this -[comment](http://www.reddit.com/r/scheme/comments/1k739l/guile_2d_game_programming_lib_for_scheme/cbmnyuk). There -are two libraries needed to perform nice font rendering with proper -internationalization support: [Pango](http://www.pango.org/), “a -library for laying out and rendering of text, with an emphasis on -internationalization,” and [Cairo](http://cairographics.org/), “a 2D -graphics library with support for multiple output devices.” - -It took me awhile to put together all of the pieces and build a -working sample program. The goal of this post is to help others that -may be trying to accomplish a similar task that have no prior -knowledge of Pango and Cairo. I will assume basic knowledge of C, SDL, -and OpenGL throughout this post. - -Let’s get the basic SDL and OpenGL initialization out of the way: - -```c -#include <pango/pangocairo.h> -#include <SDL.h> -#include <SDL_opengl.h> - -#define WINDOW_WIDTH 800 -#define WINDOW_HEIGHT 600 -#define FONT "Sans Bold 18" -#define TEXT "The quick brown fox is so かわいい!" - -void -init_sdl () -{ - SDL_Init (SDL_INIT_EVERYTHING); - SDL_SetVideoMode (WINDOW_WIDTH, WINDOW_HEIGHT, 0, SDL_OPENGL); -} - -void -init_gl () -{ - glClearColor (0.0f, 0.0f, 0.0f, 0.0f); - glDisable (GL_DEPTH_TEST); - glEnable (GL_BLEND); - glBlendFunc (GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA); - glEnable (GL_TEXTURE_2D); - glViewport (0, 0, WINDOW_WIDTH, WINDOW_HEIGHT); - glMatrixMode (GL_PROJECTION); - glLoadIdentity (); - glOrtho (0, WINDOW_WIDTH, WINDOW_HEIGHT, 0, -1, 1); - glMatrixMode (GL_MODELVIEW); - glLoadIdentity (); -} -``` - -`create_texture` simply creates an OpenGL texture given an array of -pixel data and the texture dimensions. Our Cairo surface will use BGRA -color. - -```c -unsigned int -create_texture (unsigned int width, - unsigned int height, - unsigned char *pixels) -{ - unsigned int texture_id; - - glGenTextures (1, &texture_id); - glBindTexture (GL_TEXTURE_2D, texture_id); - glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); - glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); - glTexImage2D (GL_TEXTURE_2D, - 0, - GL_RGBA, - width, - height, - 0, - GL_BGRA, - GL_UNSIGNED_BYTE, - pixels); - - return texture_id; -} -``` - -`draw_texture` clears the screen, renders a simple textured quad using -OpenGL’s immediate mode, and then swaps buffers. - -```c -void -draw_texture (int width, - int height, - unsigned int texture_id) -{ - /* Render a texture in immediate mode. */ - glMatrixMode (GL_MODELVIEW); - glLoadIdentity (); - glClear (GL_COLOR_BUFFER_BIT); - glPushMatrix (); - glBindTexture (GL_TEXTURE_2D, texture_id); - glColor3f (1.f, 1.0f, 1.0f); - - glBegin (GL_QUADS); - glTexCoord2f (0.0f, 0.0f); - glVertex2f (0.0f, 0.0f); - glTexCoord2f (1.0f, 0.0f); - glVertex2f (width, 0.0f); - glTexCoord2f (1.0f, 1.0f); - glVertex2f (width , height); - glTexCoord2f (0.0f, 1.0f); - glVertex2f (0.0f, height); - glEnd (); - - glPopMatrix (); - SDL_GL_SwapBuffers(); -} -``` - -`create_cairo_context` is used to make a new Cairo context that draws -to a raw data surface. The return value, a `cairo_t`, is the main -object in Cairo. All drawing is done via a `cairo_t` object. A -context needs a surface to draw on. -`cairo_image_surface_create_for_data` creates a raw data surface for -us. We will be translating the surface into a texture later on. - -```c -cairo_t* -create_cairo_context (int width, - int height, - int channels, - cairo_surface_t** surf, - unsigned char** buffer) -{ - *buffer = calloc (channels * width * height, sizeof (unsigned char)); - *surf = cairo_image_surface_create_for_data (*buffer, - CAIRO_FORMAT_ARGB32, - width, - height, - channels * width); - return cairo_create (*surf); -} -``` - -`create_layout_context` also makes a new Cairo context, but this -context is for PangoLayout objects. In Pango, a layout describes the -style of a paragraph of text. The layout needs a context in order to -function. We use `cairo_image_surface_create` with dimensions of 0x0 -because we won’t actually be rendering to this surface. Instead, we -will layout our text and use `create_cairo_context` to build a context -with a surface that is the size of the rendered text. Cairo uses -reference counting for dynamically allocated objects, so we need to -call `cairo_surface_destroy` when we’re done with the temporary -surface. The context still maintains a reference to the surface, so -the memory for the surface will not be freed until the context is. - -```c -cairo_t* -create_layout_context () -{ - cairo_surface_t *temp_surface; - cairo_t *context; - - temp_surface = cairo_image_surface_create (CAIRO_FORMAT_ARGB32, 0, 0); - context = cairo_create (temp_surface); - cairo_surface_destroy (temp_surface); - - return context; -} -``` - -`get_text_size` tells us the size of the text that’s in the layout, in -pixels. Pango’s units are not in pixels, so we must divide by -`PANGO_SCALE` in order to get pixel units. - -```c - -void -get_text_size (PangoLayout *layout, - unsigned int *width, - unsigned int *height) -{ - pango_layout_get_size (layout, width, height); - /* Divide by pango scale to get dimensions in pixels. */ - *width /= PANGO_SCALE; - *height /= PANGO_SCALE; -} -``` - -`render_text` is where all of the magic happens. First, we create a -layout with a layout context and set the text that we will render with -this layout. `TEXT` is defined earlier in the program as "The quick -brown fox is so かわいい!" - -Then we create a `PangoFontDescription` object. This object -represents the font that we want to render. Earlier in the program, -`FONT` is defined as "Sans Bold 18". Pango is able to figure out how -to load a font from a string in this format. Your system must be able -to recognize the font family and font face, though. I haven’t yet -figured out how to have Pango render an arbitrary font from a `*.ttf` -file. - -Next, we create a rendering context by getting the layout’s size and -creating a context with a surface big enough to show all of the -rendered text. - -Finally, we set the font color to white, render the text to the -surface with `pango_cairo_show_layout`, and create an OpenGL texture -from the surface. We also clean up all the objects that we no longer -need before returning. - -```c -unsigned int -render_text (const char *text, - unsigned int *text_width, - unsigned int *text_height, - unsigned int *texture_id) -{ - cairo_t *layout_context; - cairo_t *render_context; - cairo_surface_t *temp_surface; - cairo_surface_t *surface; - unsigned char* surface_data = NULL; - PangoFontDescription *desc; - PangoLayout *layout; - - layout_context = create_layout_context (); - - /* Create a PangoLayout, set the font and text */ - layout = pango_cairo_create_layout (layout_context); - pango_layout_set_text (layout, text, -1); - - /* Load the font */ - desc = pango_font_description_from_string (FONT); - pango_layout_set_font_description (layout, desc); - pango_font_description_free (desc); - - /* Get text dimensions and create a context to render to */ - get_text_size (layout, text_width, text_height); - render_context = create_cairo_context (*text_width, - *text_height, - 4, - &surface, - &surface_data); - - /* Render */ - cairo_set_source_rgba (render_context, 1, 1, 1, 1); - pango_cairo_show_layout (render_context, layout); - *texture_id = create_texture(*text_width, *text_height, surface_data); - - /* Clean up */ - free (surface_data); - g_object_unref (layout); - cairo_destroy (layout_context); - cairo_destroy (render_context); - cairo_surface_destroy (surface); -} -``` - -`main` is pretty simple. We initialize SDL and OpenGL, render text -to a texture, and enter the rendering loop. The program will run -until you click the close button, press "enter", or press "q". - -```c -int main (int argc, char **argv) -{ - SDL_Event event; - int keep_running = 1; - unsigned int texture_id; - unsigned int text_width = 0; - unsigned int text_height = 0; - - init_sdl (); - init_gl (); - render_text(TEXT, - &texture_id, - &text_width, - &text_height); - - /* Update/render loop */ - while (keep_running) { - SDL_PollEvent (&event); - - switch (event.type) { - case SDL_QUIT : - keep_running = 0; - break; - - case SDL_KEYDOWN : - if (event.key.keysym.sym == SDLK_ESCAPE) - keep_running = 0; - if (event.key.keysym.sym == SDLK_q) - keep_running = 0; - break; - } - - draw_texture (texture_id, text_width, text_height); - SDL_Delay (16); - } - - /* Clean up */ - glDeleteTextures (1, &texture_id); - - SDL_Quit(); - - return 0; -} -``` - -And we’re done! You should now be able to render some text in an -OpenGL context. I hope this brief tutorial was helpful. Font rendering -isn’t easy, and it’s not really my area of interest. I’m glad that -Pango exists to do all of the real work for me so that I can more -quickly move on to the parts of graphics programming that I actually -enjoy. - -You can download the full source code [here](/src/pangocairo.tar.gz). |