Stabilize auto-resize

The window dimensions are integers, so resizing to fit the content may
not be exact.

When computing the optimal size, it could cause to reduce the width and
height alternatively by few pixels, making the "optimal size" unstable.

For the same reason, during rendering, the content size could be
different from the optimal window size, leading to black borders
(supposed to be removed in optimal size).

To avoid this problem, always choose the same dimension if the choice to
resize the width or the height is in the error range.

app/src/input_manager.c

@@ -7,33 +7,6 @@
 #include "util/lock.h"
 #include "util/log.h"
 
-// Convert window coordinates (as provided by SDL_GetMouseState() to renderer
-// coordinates (as provided in SDL mouse events)
-//
-// See my question:
-// <https://stackoverflow.com/questions/49111054/how-to-get-mouse-position-on-mouse-wheel-event>
-static void
-convert_to_renderer_coordinates(SDL_Renderer *renderer, int *x, int *y) {
-    SDL_Rect viewport;
-    float scale_x, scale_y;
-    SDL_RenderGetViewport(renderer, &viewport);
-    SDL_RenderGetScale(renderer, &scale_x, &scale_y);
-    *x = (int) (*x / scale_x) - viewport.x;
-    *y = (int) (*y / scale_y) - viewport.y;
-}
-
-static struct point
-get_mouse_point(struct screen *screen) {
-    int x;
-    int y;
-    SDL_GetMouseState(&x, &y);
-    convert_to_renderer_coordinates(screen->renderer, &x, &y);
-    return (struct point) {
-        .x = x,
-        .y = y,
-    };
-}
-
 static const int ACTION_DOWN = 1;
 static const int ACTION_UP = 1 << 1;
 
@@ -487,11 +460,17 @@ convert_touch(const SDL_TouchFingerEvent *from, struct screen *screen,
 
     to->inject_touch_event.pointer_id = from->fingerId;
     to->inject_touch_event.position.screen_size = screen->frame_size;
+
+    int ww;
+    int wh;
+    SDL_GL_GetDrawableSize(screen->window, &ww, &wh);
+
     // SDL touch event coordinates are normalized in the range [0; 1]
-    float x = from->x * screen->content_size.width;
+    int32_t x = from->x * ww;
-    float y = from->y * screen->content_size.height;
+    int32_t y = from->y * wh;
     to->inject_touch_event.position.point =
         screen_convert_to_frame_coords(screen, x, y);
+
     to->inject_touch_event.pressure = from->pressure;
     to->inject_touch_event.buttons = 0;
     return true;
@@ -508,13 +487,6 @@ input_manager_process_touch(struct input_manager *im,
     }
 }
 
-static bool
-is_outside_device_screen(struct input_manager *im, int x, int y)
-{
-    return x < 0 || x >= im->screen->content_size.width ||
-           y < 0 || y >= im->screen->content_size.height;
-}
-
 static bool
 convert_mouse_button(const SDL_MouseButtonEvent *from, struct screen *screen,
                      struct control_msg *to) {
@@ -552,10 +524,14 @@ input_manager_process_mouse_button(struct input_manager *im,
             action_home(im->controller, ACTION_DOWN | ACTION_UP);
             return;
         }
+
         // double-click on black borders resize to fit the device screen
         if (event->button == SDL_BUTTON_LEFT && event->clicks == 2) {
-            bool outside =
+            int x = event->x;
-                is_outside_device_screen(im, event->x, event->y);
+            int y = event->y;
+            SDL_Rect *r = &im->screen->rect;
+            bool outside = x < r->x || x >= r->x + r->w
+                        || y < r->y || y >= r->y + r->h;
             if (outside) {
                 screen_resize_to_fit(im->screen);
                 return;
@@ -579,9 +555,15 @@ input_manager_process_mouse_button(struct input_manager *im,
 static bool
 convert_mouse_wheel(const SDL_MouseWheelEvent *from, struct screen *screen,
                     struct control_msg *to) {
+
+    // mouse_x and mouse_y are expressed in pixels relative to the window
+    int mouse_x;
+    int mouse_y;
+    SDL_GetMouseState(&mouse_x, &mouse_y);
+
     struct position position = {
         .screen_size = screen->frame_size,
-        .point = get_mouse_point(screen),
+        .point = screen_convert_to_frame_coords(screen, mouse_x, mouse_y),
     };
 
     to->type = CONTROL_MSG_TYPE_INJECT_SCROLL_EVENT;

app/src/screen.c

@@ -87,6 +87,26 @@ get_preferred_display_bounds(struct size *bounds) {
     return true;
 }
 
+// Indicate if the width should be kept on computing the optimal rectangle size
+// to display the content in the window.
+// Return true if the width should be kept, false if the height should be kept.
+static bool
+should_keep_width(struct size window_size, struct size content_size) {
+    // 32 bits because we need to multiply two 16 bits values
+    uint32_t ww = window_size.width;
+    uint32_t wh = window_size.height;
+    uint32_t cw = content_size.width;
+    uint32_t ch = content_size.height;
+
+    // To avoid keeping alternatively width and height on successive resizes
+    // due to rounding to integer, always prefer height (arbitrarily) if in the
+    // error range.
+
+    // err = ceil of content aspect ratio
+    unsigned err = (cw + ch - 1) / ch;
+    return cw * wh > ch * (ww + err);
+}
+
 // return the optimal size of the window, with the following constraints:
 //  - it attempts to keep at least one dimension of the current_size (i.e. it
 //    crops the black borders)
@@ -99,33 +119,33 @@ get_optimal_size(struct size current_size, struct size content_size) {
         return current_size;
     }
 
-    struct size display_size;
+    struct size window_size;
-    // 32 bits because we need to multiply two 16 bits values
-    uint32_t w;
-    uint32_t h;
 
+    struct size display_size;
     if (!get_preferred_display_bounds(&display_size)) {
         // could not get display bounds, do not constraint the size
-        w = current_size.width;
+        window_size.width = current_size.width;
-        h = current_size.height;
+        window_size.height = current_size.height;
     } else {
-        w = MIN(current_size.width, display_size.width);
+        window_size.width = MIN(current_size.width, display_size.width);
-        h = MIN(current_size.height, display_size.height);
+        window_size.height = MIN(current_size.height, display_size.height);
     }
 
-    bool keep_width = content_size.width * h > content_size.height * w;
+    bool keep_width = should_keep_width(window_size, content_size);
     if (keep_width) {
         // remove black borders on top and bottom
-        h = content_size.height * w / content_size.width;
+        window_size.height = content_size.height * window_size.width
+                           / content_size.width;
     } else {
         // remove black borders on left and right (or none at all if it already
         // fits)
-        w = content_size.width * h / content_size.height;
+        window_size.width = content_size.width * window_size.height
+                          / content_size.height;
     }
 
-    // w and h must fit into 16 bits
+    // width and height must fit into 16 bits
-    assert(w < 0x10000 && h < 0x10000);
+    assert(window_size.width < 0x10000 && window_size.height < 0x10000);
-    return (struct size) {w, h};
+    return window_size;
 }
 
 // same as get_optimal_size(), but read the current size from the window
@@ -162,6 +182,34 @@ get_initial_optimal_size(struct size content_size, uint16_t req_width,
     return window_size;
 }
 
+static void
+update_content_rect(struct screen *screen) {
+    int w;
+    int h;
+    SDL_GL_GetDrawableSize(screen->window, &w, &h);
+
+    struct size window_size = {w, h};
+    uint16_t ww = window_size.width;
+    uint16_t wh = window_size.height;
+    uint16_t cw = screen->content_size.width;
+    uint16_t ch = screen->content_size.height;
+
+    SDL_Rect *rect = &screen->rect;
+
+    bool keep_width = should_keep_width(window_size, screen->content_size);
+    if (keep_width) {
+        rect->x = 0;
+        rect->w = ww;
+        rect->h = ww * ch / cw;
+        rect->y = (wh - rect->h) / 2;
+    } else {
+        rect->y = 0;
+        rect->h = wh;
+        rect->w = wh * cw / ch;
+        rect->x = (ww - rect->w) / 2;
+    }
+}
+
 void
 screen_init(struct screen *screen) {
     *screen = (struct screen) SCREEN_INITIALIZER;
@@ -251,13 +299,6 @@ screen_init_rendering(struct screen *screen, const char *window_title,
     const char *renderer_name = r ? NULL : renderer_info.name;
     LOGI("Renderer: %s", renderer_name ? renderer_name : "(unknown)");
 
-    if (SDL_RenderSetLogicalSize(screen->renderer, content_size.width,
-                                 content_size.height)) {
-        LOGE("Could not set renderer logical size: %s", SDL_GetError());
-        screen_destroy(screen);
-        return false;
-    }
-
     // stats with "opengl"
     screen->use_opengl = renderer_name && !strncmp(renderer_name, "opengl", 6);
     if (screen->use_opengl) {
@@ -335,13 +376,6 @@ screen_set_rotation(struct screen *screen, unsigned rotation) {
     struct size new_content_size =
         get_rotated_size(screen->frame_size, rotation);
 
-    if (SDL_RenderSetLogicalSize(screen->renderer,
-                                 new_content_size.width,
-                                 new_content_size.height)) {
-        LOGE("Could not set renderer logical size: %s", SDL_GetError());
-        return;
-    }
-
     struct size windowed_size = get_windowed_window_size(screen);
     struct size target_size = {
         .width = (uint32_t) windowed_size.width * new_content_size.width
@@ -356,6 +390,7 @@ screen_set_rotation(struct screen *screen, unsigned rotation) {
     screen->rotation = rotation;
     LOGI("Display rotation set to %u", rotation);
 
+    update_content_rect(screen);
     screen_render(screen);
 }
 
@@ -364,18 +399,11 @@ static bool
 prepare_for_frame(struct screen *screen, struct size new_frame_size) {
     if (screen->frame_size.width != new_frame_size.width
             || screen->frame_size.height != new_frame_size.height) {
-        struct size new_content_size =
-            get_rotated_size(new_frame_size, screen->rotation);
-        if (SDL_RenderSetLogicalSize(screen->renderer,
-                                     new_content_size.width,
-                                     new_content_size.height)) {
-            LOGE("Could not set renderer logical size: %s", SDL_GetError());
-            return false;
-        }
-
         // frame dimension changed, destroy texture
         SDL_DestroyTexture(screen->texture);
 
+        struct size new_content_size =
+            get_rotated_size(new_frame_size, screen->rotation);
         struct size content_size = screen->content_size;
         struct size windowed_size = get_windowed_window_size(screen);
         struct size target_size = {
@@ -427,6 +455,7 @@ screen_update_frame(struct screen *screen, struct video_buffer *vb) {
         mutex_unlock(vb->mutex);
         return false;
     }
+    update_content_rect(screen);
     update_texture(screen, frame);
     mutex_unlock(vb->mutex);
 
@@ -434,11 +463,17 @@ screen_update_frame(struct screen *screen, struct video_buffer *vb) {
     return true;
 }
 
+void
+screen_window_resized(struct screen *screen) {
+    update_content_rect(screen);
+    screen_render(screen);
+}
+
 void
 screen_render(struct screen *screen) {
     SDL_RenderClear(screen->renderer);
     if (screen->rotation == 0) {
-        SDL_RenderCopy(screen->renderer, screen->texture, NULL, NULL);
+        SDL_RenderCopy(screen->renderer, screen->texture, NULL, &screen->rect);
     } else {
         // rotation in RenderCopyEx() is clockwise, while screen->rotation is
         // counterclockwise (to be consistent with --lock-video-orientation)
@@ -448,12 +483,14 @@ screen_render(struct screen *screen) {
         SDL_Rect *dstrect = NULL;
         SDL_Rect rect;
         if (screen->rotation & 1) {
-            struct size size = screen->content_size;
+            rect.x = screen->rect.x + (screen->rect.w - screen->rect.h) / 2;
-            rect.x = (size.width - size.height) / 2;
+            rect.y = screen->rect.y + (screen->rect.h - screen->rect.w) / 2;
-            rect.y = (size.height - size.width) / 2;
+            rect.w = screen->rect.h;
-            rect.w = size.height;
+            rect.h = screen->rect.w;
-            rect.h = size.width;
             dstrect = &rect;
+        } else {
+            assert(screen->rotation == 2);
+            dstrect = &screen->rect;
         }
 
         SDL_RenderCopyEx(screen->renderer, screen->texture, NULL, dstrect,
@@ -532,7 +569,7 @@ screen_handle_window_event(struct screen *screen,
                 // window is maximized or fullscreen is enabled.
                 screen->windowed_window_size = get_window_size(screen->window);
             }
-            screen_render(screen);
+            screen_window_resized(screen);
             break;
         case SDL_WINDOWEVENT_MAXIMIZED:
             // The backup size must be non-nul.
@@ -561,6 +598,12 @@ screen_convert_to_frame_coords(struct screen *screen, int32_t x, int32_t y) {
 
     int32_t w = screen->content_size.width;
     int32_t h = screen->content_size.height;
+
+    // scale
+    x = (x - screen->rect.x) * w / screen->rect.w;
+    y = (y - screen->rect.y) * h / screen->rect.h;
+
+    // rotate
     struct point result;
     switch (rotation) {
         case 0:

app/src/screen.h

@@ -28,6 +28,8 @@ struct screen {
     struct size windowed_window_size_backup;
     // client rotation: 0, 1, 2 or 3 (x90 degrees counterclockwise)
     unsigned rotation;
+    // rectangle of the content (excluding black borders)
+    struct SDL_Rect rect;
     bool has_frame;
     bool fullscreen;
     bool maximized;
@@ -58,6 +60,12 @@ struct screen {
         .height = 0, \
     }, \
     .rotation = 0, \
+    .rect = { \
+        .x = 0, \
+        .y = 0, \
+        .w = 0, \
+        .h = 0, \
+    }, \
     .has_frame = false, \
     .fullscreen = false, \
     .maximized = false, \
@@ -90,6 +98,10 @@ screen_destroy(struct screen *screen);
 bool
 screen_update_frame(struct screen *screen, struct video_buffer *vb);
 
+// update content after window resizing
+void
+screen_window_resized(struct screen *screen);
+
 // render the texture to the renderer
 void
 screen_render(struct screen *screen);