Only allow images to exist on a single page (#141)

At the moment we list the data for every image with every page, even if they're not used on that page. Make it so that images can exist on only one page. This avoids massive redundancy where information about every image is stored with every page, even when they're not used. Documents with either lots of images, or lots of pages (or both) will benefit most from this.

In theory in the future we might want to allow the same image to exist multiple times, but the API doesn't really allow for that at the moment anyway, so this is simpler.

pdfgen.c

@@ -256,7 +256,10 @@ struct pdf_object {
             struct pdf_object *parent;
             struct flexarray children;
         } bookmark;
-        struct dstr stream;
+        struct {
+            struct pdf_object *page;
+            struct dstr stream;
+        } stream;
         struct {
             float width;
             float height;
@@ -640,7 +643,7 @@ static void pdf_object_destroy(struct pdf_object *object)
     switch (object->type) {
     case OBJ_stream:
     case OBJ_image:
-        dstr_free(&object->stream);
+        dstr_free(&object->stream.stream);
         break;
     case OBJ_page:
         flexarray_clear(&object->page.children);
@@ -926,7 +929,8 @@ static int pdf_save_object(struct pdf_doc *pdf, FILE *fp, int index)
     switch (object->type) {
     case OBJ_stream:
     case OBJ_image: {
-        fwrite(dstr_data(&object->stream), dstr_len(&object->stream), 1, fp);
+        fwrite(dstr_data(&object->stream.stream),
+               dstr_len(&object->stream.stream), 1, fp);
         break;
     }
     case OBJ_info: {
@@ -951,7 +955,7 @@ static int pdf_save_object(struct pdf_doc *pdf, FILE *fp, int index)
 
     case OBJ_page: {
         struct pdf_object *pages = pdf_find_first_object(pdf, OBJ_pages);
-        struct pdf_object *image = pdf_find_first_object(pdf, OBJ_image);
+        bool printed_xobjects = false;
 
         fprintf(fp,
                 "<<\r\n"
@@ -975,13 +979,19 @@ static int pdf_save_object(struct pdf_doc *pdf, FILE *fp, int index)
         }
         fprintf(fp, "    >>\r\n");
 
-        if (image) {
-            fprintf(fp, "    /XObject <<");
-            for (; image; image = image->next)
+        for (struct pdf_object *image = pdf_find_first_object(pdf, OBJ_image);
+             image; image = image->next) {
+            if (image->stream.page == object) {
+                if (!printed_xobjects) {
+                    fprintf(fp, "    /XObject <<");
+                    printed_xobjects = true;
+                }
                 fprintf(fp, "      /Image%d %d 0 R ", image->index,
                         image->index);
-            fprintf(fp, "    >>\r\n");
+            }
         }
+        if (printed_xobjects)
+            fprintf(fp, "    >>\r\n");
         fprintf(fp, "  >>\r\n");
 
         fprintf(fp, "  /Contents [\r\n");
@@ -1258,9 +1268,9 @@ static int pdf_add_stream(struct pdf_doc *pdf, struct pdf_object *page,
     if (!obj)
         return pdf->errval;
 
-    dstr_printf(&obj->stream, "<< /Length %zu >>stream\r\n", len);
-    dstr_append_data(&obj->stream, buffer, len);
-    dstr_append(&obj->stream, "\r\nendstream\r\n");
+    dstr_printf(&obj->stream.stream, "<< /Length %zu >>stream\r\n", len);
+    dstr_append_data(&obj->stream.stream, buffer, len);
+    dstr_append(&obj->stream.stream, "\r\nendstream\r\n");
 
     return flexarray_append(&page->page.children, obj);
 }
@@ -3206,7 +3216,7 @@ static pdf_object *pdf_add_raw_grayscale8(struct pdf_doc *pdf,
         dstr_free(&str);
         return NULL;
     }
-    obj->stream = str;
+    obj->stream.stream = str;
 
     return obj;
 }
@@ -3249,7 +3259,7 @@ static struct pdf_object *pdf_add_raw_rgb24(struct pdf_doc *pdf,
         dstr_free(&str);
         return NULL;
     }
-    obj->stream = str;
+    obj->stream.stream = str;
 
     return obj;
 }
@@ -3306,7 +3316,7 @@ pdf_add_raw_jpeg_data(struct pdf_doc *pdf, const struct pdf_img_info *info,
     if (!obj)
         return NULL;
 
-    dstr_printf(&obj->stream,
+    dstr_printf(&obj->stream.stream,
                 "<<\r\n"
                 "  /Type /XObject\r\n"
                 "  /Name /Image%d\r\n"
@@ -3321,9 +3331,9 @@ pdf_add_raw_jpeg_data(struct pdf_doc *pdf, const struct pdf_img_info *info,
                 flexarray_size(&pdf->objects),
                 (info->jpeg.ncolours == 1) ? "/DeviceGray" : "/DeviceRGB",
                 info->width, info->height, len);
-    dstr_append_data(&obj->stream, jpeg_data, len);
+    dstr_append_data(&obj->stream.stream, jpeg_data, len);
 
-    dstr_printf(&obj->stream, "\r\nendstream\r\n");
+    dstr_printf(&obj->stream.stream, "\r\nendstream\r\n");
 
     return obj;
 }
@@ -3375,6 +3385,22 @@ static int pdf_add_image(struct pdf_doc *pdf, struct pdf_object *page,
     int ret;
     struct dstr str = INIT_DSTR;
 
+    if (!page)
+        page = pdf_find_last_object(pdf, OBJ_page);
+
+    if (!page)
+        return pdf_set_err(pdf, -EINVAL, "Invalid pdf page");
+
+    if (image->type != OBJ_image)
+        return pdf_set_err(pdf, -EINVAL,
+                           "adding an image, but wrong object type %d",
+                           image->type);
+
+    if (image->stream.page != NULL)
+        return pdf_set_err(pdf, -EEXIST, "image already on a page");
+
+    image->stream.page = page;
+
     dstr_append(&str, "q ");
     dstr_printf(&str, "%f 0 0 %f %f %f cm ", width, height, x, y);
     dstr_printf(&str, "/Image%d Do ", image->index);
@@ -3880,7 +3906,7 @@ static int pdf_add_png_data(struct pdf_doc *pdf, struct pdf_object *page,
         goto free_buffers;
     }
 
-    dstr_append_data(&obj->stream, final_data, written);
+    dstr_append_data(&obj->stream.stream, final_data, written);
 
     if (get_img_display_dimensions(pdf, header->width, header->height,
                                    &display_width, &display_height)) {