Introduce interface to backends

Functions twin_{create,destroy} are introduced along with the refined
backend interface, allowing for an incoming Linux framebuffer backend.
This commit simplifies backend development and consolidates consistent
APIs, meaning that a single source can be built for supported backends
without conditional compilation.

Author: jserv

Makefile

@@ -1,7 +1,7 @@
 # FIXME: make these entries configurable
-CONFIG_BACKEND_SDL := y
-CONFIG_LOADER_JPEG := y
-CONFIG_LOADER_PNG := y
+CONFIG_BACKEND_SDL ?= y
+CONFIG_LOADER_JPEG ?= y
+CONFIG_LOADER_PNG ?= y
 
 # Rules
 
@@ -10,9 +10,9 @@ target.o-y :=
 TARGET_LIBS :=
 
 target.a-y = \
-	libbackend.a \
 	libapps.a \
-	libtwin.a
+	libtwin.a \
+	libbackend.a
 
 # Core library
 
@@ -46,7 +46,8 @@ libtwin.a_files-y = \
 	src/hull.c \
 	src/icon.c \
 	src/pixmap.c \
-	src/timeout.c
+	src/timeout.c \
+	src/api.c
 
 libtwin.a_includes-y := include
 
@@ -77,32 +78,28 @@ libapps.a_files-y = \
 libapps.a_includes-y := include
 
 # Graphical backends
+BACKEND := none
 
 libbackend.a_files-y :=
 libbackend.a_cflags-y :=
-libbackend.a_includes-y := include
+libbackend.a_includes-y := \
+	include \
+	src
 
 ifeq ($(CONFIG_BACKEND_SDL), y)
+BACKEND = sdl
 libbackend.a_files-y += backend/sdl.c
 libbackend.a_cflags-y += $(shell sdl2-config --cflags)
 TARGET_LIBS += $(shell sdl2-config --libs)
 endif
 
 # Platform-specific executables
-
-ifeq ($(CONFIG_BACKEND_SDL), y)
-target-y += demo-sdl
-
-demo-sdl_depends-y += $(target.a-y)
-demo-sdl_files-y = \
-	apps/twin-sdl.c
-
-demo-sdl_includes-y := include
-demo-sdl_includes-y += backend
-
-demo-sdl_cflags-y = $(shell sdl2-config --cflags)
-demo-sdl_ldflags-y := $(target.a-y)
-demo-sdl_ldflags-y += $(TARGET_LIBS)
-endif # CONFIG_BACKEND_SDL
+target-y += demo-$(BACKEND)
+demo-$(BACKEND)_depends-y += $(target.a-y)
+demo-$(BACKEND)_files-y = apps/main.c
+demo-$(BACKEND)_includes-y := include
+demo-$(BACKEND)_ldflags-y := \
+	$(target.a-y) \
+	$(TARGET_LIBS)
 
 include mk/common.mk

apps/twin-sdl.c renamed to apps/main.c

@@ -11,8 +11,6 @@
 #include <time.h>
 #include <unistd.h>
 
-#include "twin_sdl.h"
-
 #include "apps_calc.h"
 #include "apps_clock.h"
 #include "apps_demo.h"
@@ -70,18 +68,20 @@ static twin_pixmap_t *load_background(twin_screen_t *screen,
 
 int main(void)
 {
-    twin_sdl_t *sdl = twin_sdl_create(WIDTH, HEIGHT);
+    twin_context_t *x = twin_create(WIDTH, HEIGHT);
 
     twin_screen_set_background(
-        sdl->screen, load_background(sdl->screen, ASSET_PATH "/tux.png"));
+        x->screen, load_background(x->screen, ASSET_PATH "/tux.png"));
 
-    apps_demo_start(sdl->screen, "Demo", 100, 100, 400, 400);
-    apps_hello_start(sdl->screen, "Hello, World", 0, 0, 200, 200);
-    apps_clock_start(sdl->screen, "Clock", 10, 10, 200, 200);
-    apps_calc_start(sdl->screen, "Calculator", 100, 100, 200, 200);
-    apps_line_start(sdl->screen, "Line", 0, 0, 200, 200);
-    apps_spline_start(sdl->screen, "Spline", 20, 20, 400, 400);
+    apps_demo_start(x->screen, "Demo", 100, 100, 400, 400);
+    apps_hello_start(x->screen, "Hello, World", 0, 0, 200, 200);
+    apps_clock_start(x->screen, "Clock", 10, 10, 200, 200);
+    apps_calc_start(x->screen, "Calculator", 100, 100, 200, 200);
+    apps_line_start(x->screen, "Line", 0, 0, 200, 200);
+    apps_spline_start(x->screen, "Spline", 20, 20, 400, 400);
 
     twin_dispatch();
+
+    twin_destroy(x);
     return 0;
 }

backend/sdl.c

@@ -4,18 +4,31 @@
  * All rights reserved.
  */
 
+#include <SDL.h>
+#include <SDL_render.h>
 #include <stdio.h>
+#include <twin.h>
 
-#include "twin_private.h"
-#include "twin_sdl.h"
+#include "twin_backend.h"
+
+typedef struct {
+    SDL_Window *win;
+    int *pixels;
+    SDL_Renderer *render;
+    SDL_Texture *texture;
+    twin_coord_t width, height;
+    int image_y;
+} twin_sdl_t;
+
+#define PRIV(x) ((twin_sdl_t *) ((twin_context_t *) x)->priv)
 
 static void _twin_sdl_put_begin(twin_coord_t left,
                                 twin_coord_t top,
                                 twin_coord_t right,
                                 twin_coord_t bottom,
                                 void *closure)
 {
-    twin_sdl_t *tx = closure;
+    twin_sdl_t *tx = PRIV(closure);
     tx->width = right - left;
     tx->height = bottom - top;
     tx->image_y = top;
@@ -27,41 +40,55 @@ static void _twin_sdl_put_span(twin_coord_t left,
                                twin_argb32_t *pixels,
                                void *closure)
 {
-    twin_sdl_t *tx = closure;
+    twin_screen_t *screen = ((twin_context_t *) closure)->screen;
+    twin_sdl_t *tx = PRIV(closure);
 
     for (twin_coord_t ix = left, iy = top; ix < right; ix++) {
         twin_argb32_t pixel = *pixels++;
-
-        if (tx->depth == 16)
-            pixel = twin_argb32_to_rgb16(pixel);
-
-        tx->pixels[iy * tx->screen->width + ix] = pixel;
+        tx->pixels[iy * screen->width + ix] = pixel;
     }
     if ((top + 1 - tx->image_y) == tx->height) {
         SDL_UpdateTexture(tx->texture, NULL, tx->pixels,
-                          tx->screen->width * sizeof(uint32_t));
+                          screen->width * sizeof(uint32_t));
         SDL_RenderCopy(tx->render, tx->texture, NULL, NULL);
         SDL_RenderPresent(tx->render);
     }
 }
 
+static void _twin_sdl_destroy(twin_screen_t *screen, twin_sdl_t *tx)
+{
+    twin_screen_destroy(screen);
+    SDL_DestroyRenderer(tx->render);
+    SDL_DestroyWindow(tx->win);
+    SDL_Quit();
+}
+
+static void twin_sdl_damage(twin_screen_t *screen, twin_sdl_t *tx)
+{
+    int width, height;
+    SDL_GetWindowSize(tx->win, &width, &height);
+    twin_screen_damage(screen, 0, 0, width, height);
+}
+
 static bool twin_sdl_read_events(int file maybe_unused,
                                  twin_file_op_t ops maybe_unused,
                                  void *closure)
 {
-    twin_sdl_t *tx = closure;
+    twin_screen_t *screen = ((twin_context_t *) closure)->screen;
+    twin_sdl_t *tx = PRIV(closure);
+
     SDL_Event ev;
     while (SDL_PollEvent(&ev)) {
         twin_event_t tev;
         switch (ev.type) {
         case SDL_WINDOWEVENT:
             if (ev.window.event == SDL_WINDOWEVENT_EXPOSED ||
                 ev.window.event == SDL_WINDOWEVENT_SHOWN) {
-                twin_sdl_damage(tx, &ev);
+                twin_sdl_damage(screen, tx);
             }
             break;
         case SDL_QUIT:
-            twin_sdl_destroy(tx);
+            _twin_sdl_destroy(screen, tx);
             return false;
         case SDL_MOUSEBUTTONDOWN:
         case SDL_MOUSEBUTTONUP:
@@ -71,21 +98,21 @@ static bool twin_sdl_read_events(int file maybe_unused,
                 ((ev.button.state >> 8) | (1 << (ev.button.button - 1)));
             tev.kind = ((ev.type == SDL_MOUSEBUTTONDOWN) ? TwinEventButtonDown
                                                          : TwinEventButtonUp);
-            twin_screen_dispatch(tx->screen, &tev);
+            twin_screen_dispatch(screen, &tev);
             break;
         case SDL_KEYDOWN:
         case SDL_KEYUP:
             tev.u.key.key = ev.key.keysym.sym;
             tev.kind = ((ev.key.type == SDL_KEYDOWN) ? TwinEventKeyDown
                                                      : TwinEventKeyUp);
-            twin_screen_dispatch(tx->screen, &tev);
+            twin_screen_dispatch(screen, &tev);
             break;
         case SDL_MOUSEMOTION:
             tev.u.pointer.screen_x = ev.motion.x;
             tev.u.pointer.screen_y = ev.motion.y;
             tev.kind = TwinEventMotion;
             tev.u.pointer.button = ev.motion.state;
-            twin_screen_dispatch(tx->screen, &tev);
+            twin_screen_dispatch(screen, &tev);
             break;
         }
     }
@@ -94,85 +121,89 @@ static bool twin_sdl_read_events(int file maybe_unused,
 
 static bool twin_sdl_work(void *closure)
 {
-    twin_sdl_t *tx = closure;
+    twin_screen_t *screen = ((twin_context_t *) closure)->screen;
 
-    if (twin_screen_damaged(tx->screen))
-        twin_sdl_update(tx);
+    if (twin_screen_damaged(screen))
+        twin_screen_update(screen);
     return true;
 }
 
-twin_sdl_t *twin_sdl_create(int width, int height)
+twin_context_t *twin_sdl_init(int width, int height)
 {
-    static char *title = "twin-sdl";
-
-    twin_sdl_t *tx = malloc(sizeof(twin_sdl_t));
-    if (!tx)
+    twin_context_t *ctx = calloc(1, sizeof(twin_context_t));
+    if (!ctx)
+        return NULL;
+    ctx->priv = calloc(1, sizeof(twin_sdl_t));
+    if (!ctx->priv)
         return NULL;
 
-    if (SDL_Init(SDL_INIT_VIDEO) < 0)
+    if (SDL_Init(SDL_INIT_VIDEO) < 0) {
         printf("error : %s\n", SDL_GetError());
+        goto bail;
+    }
+
+    twin_sdl_t *tx = ctx->priv;
+
+    static char *title = "twin-sdl";
     tx->win = SDL_CreateWindow(title, SDL_WINDOWPOS_UNDEFINED,
                                SDL_WINDOWPOS_UNDEFINED, width, height,
                                SDL_WINDOW_SHOWN);
-    if (!tx->win)
+    if (!tx->win) {
         printf("error : %s\n", SDL_GetError());
+        goto bail;
+    }
+
     tx->pixels = malloc(width * height * sizeof(uint32_t));
     memset(tx->pixels, 255, width * height * sizeof(uint32_t));
 
     tx->render = SDL_CreateRenderer(tx->win, -1, SDL_RENDERER_ACCELERATED);
-    if (!tx->render)
+    if (!tx->render) {
         printf("error : %s\n", SDL_GetError());
+        goto bail_pixels;
+    }
     SDL_SetRenderDrawColor(tx->render, 255, 255, 255, 255);
     SDL_RenderClear(tx->render);
 
     tx->texture = SDL_CreateTexture(tx->render, SDL_PIXELFORMAT_ARGB8888,
                                     SDL_TEXTUREACCESS_STREAMING, width, height);
 
-    tx->screen = twin_screen_create(width, height, _twin_sdl_put_begin,
-                                    _twin_sdl_put_span, tx);
-
-    twin_set_file(twin_sdl_read_events, 0, TWIN_READ, tx);
+    ctx->screen = twin_screen_create(width, height, _twin_sdl_put_begin,
+                                     _twin_sdl_put_span, ctx);
 
-    twin_set_work(twin_sdl_work, TWIN_WORK_REDISPLAY, tx);
+    twin_set_file(twin_sdl_read_events, 0, TWIN_READ, ctx);
 
-    return tx;
-}
+    twin_set_work(twin_sdl_work, TWIN_WORK_REDISPLAY, ctx);
 
-void twin_sdl_destroy(twin_sdl_t *tx)
-{
-    SDL_DestroyRenderer(tx->render);
-    SDL_DestroyWindow(tx->win);
-    tx->win = 0;
-    twin_screen_destroy(tx->screen);
-    SDL_Quit();
-}
+    return ctx;
 
-void twin_sdl_damage(twin_sdl_t *tx, SDL_Event *ev maybe_unused)
-{
-    int width, height;
-    SDL_GetWindowSize(tx->win, &width, &height);
-    twin_screen_damage(tx->screen, 0, 0, width, height);
+bail_pixels:
+    free(tx->pixels);
+bail:
+    free(ctx->priv);
+    free(ctx);
+    return NULL;
 }
 
-void twin_sdl_configure(twin_sdl_t *tx, SDL_Event *ev maybe_unused)
+static void twin_sdl_configure(twin_context_t *ctx)
 {
     int width, height;
-    SDL_GetWindowSize(tx->win, &width, &height);
-    twin_screen_resize(tx->screen, width, height);
+    SDL_GetWindowSize(PRIV(ctx)->win, &width, &height);
+    twin_screen_resize(ctx->screen, width, height);
 }
 
-void twin_sdl_update(twin_sdl_t *tx)
+static void twin_sdl_exit(twin_context_t *ctx)
 {
-    twin_screen_update(tx->screen);
+    if (!ctx)
+        return;
+    free(PRIV(ctx)->pixels);
+    free(ctx->priv);
+    free(ctx);
 }
 
-bool twin_sdl_process_events(twin_sdl_t *tx)
-{
-    bool result;
+/* Register the SDL backend */
 
-    _twin_run_work();
-    result = twin_sdl_read_events(0, 0, tx);
-    _twin_run_work();
-
-    return result;
-}
+const twin_backend_t g_twin_backend = {
+    .init = twin_sdl_init,
+    .configure = twin_sdl_configure,
+    .exit = twin_sdl_exit,
+};