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experiments/cairo/cairo4.cpp

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+
+#include <cairo.h>
+
+#include <SDL.h>
+
+int main() {
+    double ang = 0,angv = (M_PI * 2) / 360,angstep = (M_PI * 2) / 4;
+
+    if (SDL_Init(SDL_INIT_VIDEO) != 0)
+        return 1;
+
+    SDL_Window *window = SDL_CreateWindow("Cairo",SDL_WINDOWPOS_UNDEFINED,SDL_WINDOWPOS_UNDEFINED,640,480,SDL_WINDOW_SHOWN);
+    if (window == NULL)
+        return 1;
+
+    SDL_Surface *surface = SDL_GetWindowSurface(window);
+    if (surface == NULL)
+        return 1;
+
+    cairo_format_t csurffmt = CAIRO_FORMAT_INVALID;
+    if (surface->format->BytesPerPixel == 4) {
+        csurffmt = CAIRO_FORMAT_ARGB32;
+    }
+    else if (surface->format->BytesPerPixel == 3) {
+        csurffmt = CAIRO_FORMAT_RGB24;
+    }
+    else if (surface->format->BytesPerPixel == 2) {
+        csurffmt = CAIRO_FORMAT_RGB16_565;
+    }
+    else {
+        return 1;
+    }
+
+    if (surface->pixels == NULL || SDL_MUSTLOCK(surface)) {
+        fprintf(stderr,"Surface not appropriate for Cairo\n");
+        return 1;
+    }
+
+    int csurfpitch = cairo_format_stride_for_width(csurffmt, 640);
+    fprintf(stderr,"Cairo stride %d\n",csurfpitch);
+    fprintf(stderr,"SDL stride %d\n",surface->pitch);
+
+    if (csurfpitch != surface->pitch) {
+        fprintf(stderr,"Sorry, Cairo and SDL do not agree\n");
+        return 1;
+    }
+
+    cairo_surface_t* csurf = cairo_image_surface_create_for_data((unsigned char*)surface->pixels, csurffmt, 640, 480, csurfpitch);
+    if (csurf == NULL)
+        return 1;
+
+    cairo_t* cactx = cairo_create(csurf);
+    if (cactx == NULL)
+        return 1;
+
+    bool run = true;
+    while (run) {
+        SDL_Event ev;
+
+        while (SDL_PollEvent(&ev)) {
+            switch (ev.type) {
+                case SDL_WINDOWEVENT:
+                    switch (ev.window.event) {
+                        case SDL_WINDOWEVENT_CLOSE:
+                            run = false;
+                            break;
+                    }
+                    break;
+                case SDL_KEYDOWN:
+                    switch (ev.key.keysym.sym) {
+                        case SDLK_ESCAPE:
+                            run = false;
+                            break;
+                    }
+                    break;
+            }
+        }
+
+        // clear
+        cairo_reset_clip(cactx);
+        cairo_set_source_rgb(cactx,0.25,0.25,0.25);
+        cairo_paint(cactx);
+
+        // draw
+        cairo_set_line_width(cactx,8.0);
+
+        {
+            unsigned int step=0;
+
+            for (double a=0;a < (M_PI * 2);a += angstep,step++) {
+                double x = 320.0 + cos(a+ang)*200.0 + 40;
+                double y = 240.0 + sin(a+ang)*200.0 + 40;
+
+                if (step == 0)
+                    cairo_move_to(cactx,x,y);
+                else
+                    cairo_line_to(cactx,x,y);
+            }
+
+            cairo_close_path(cactx);
+            ang += angv;
+        }
+
+        cairo_set_source_rgba(cactx,0,0,0,0.5);
+        cairo_fill(cactx);
+
+        {
+            unsigned int step=0;
+
+            for (double a=0;a < (M_PI * 2);a += angstep,step++) {
+                double x = 320.0 + cos(a+ang)*200.0;
+                double y = 240.0 + sin(a+ang)*200.0;
+
+                if (step == 0)
+                    cairo_move_to(cactx,x,y);
+                else
+                    cairo_line_to(cactx,x,y);
+            }
+
+            cairo_close_path(cactx);
+            ang += angv;
+        }
+
+        cairo_set_source_rgb(cactx,1.0,1.0,1.0);
+        cairo_fill_preserve(cactx);
+
+        cairo_set_source_rgb(cactx,0.0,0.0,1.0);
+        cairo_stroke(cactx);
+
+        // copy Cairo output to display
+        cairo_surface_flush(csurf);
+
+        SDL_UpdateWindowSurface(window);
+
+        SDL_Delay(1000 / 30);
+    }
+
+    cairo_surface_flush(csurf);
+    cairo_destroy(cactx);
+    cairo_surface_destroy(csurf);
+
+    // do not free surface, owned by dinwo
+    SDL_DestroyWindow(window);
+    SDL_Quit();
+    return 0;
+}
+