Mention mipmapping in FAQ

Add an option to disable trilinear filtering even if mipmapping is
available.

FAQ.md

@@ -134,18 +134,27 @@ that's all. See [#37].
 
 ### The quality is low
 
-On Windows, you may need to configure the [scaling behavior].
+If the definition of your client window is smaller than that of your device
+screen, then you might get poor quality, especially visible on text (see [#40]).
+
+[#40]: https://github.com/Genymobile/scrcpy/issues/40
+
+To improve downscaling quality, trilinear filtering is enabled automatically
+if the renderer is OpenGL and if it supports mipmapping.
+
+On Windows or macOS, you might need to force OpenGL:
+
+```
+scrcpy --render-driver=opengl
+```
+
+On Windows, you may also need to configure the [scaling behavior].
 
 > `scrcpy.exe` > Properties > Compatibility > Change high DPI settings >
 > Override high DPI scaling behavior > Scaling performed by: _Application_.
 
 [scaling behavior]: https://github.com/Genymobile/scrcpy/issues/40#issuecomment-424466723
 
-If the definition of your client window is far smaller than that of your device
-screen, then you'll get poor quality. This is especially visible on text. See
-[#40].
-
-[#40]: https://github.com/Genymobile/scrcpy/issues/40
 
 
 ### KWin compositor crashes

app/meson.build

@@ -11,6 +11,7 @@ src = [
     'src/file_handler.c',
     'src/fps_counter.c',
     'src/input_manager.c',
+    'src/opengl.c',
     'src/receiver.c',
     'src/recorder.c',
     'src/scrcpy.c',

app/scrcpy.1

@@ -74,6 +74,10 @@ Disable device control (mirror the device in read\-only).
 .B \-N, \-\-no\-display
 Do not display device (only when screen recording is enabled).
 
+.TP
+.B \-\-no\-mipmaps
+If the renderer is OpenGL 3.0+ or OpenGL ES 2.0+, then mipmaps are automatically generated to improve downscaling quality. This option disables the generation of mipmaps.
+
 .TP
 .BI "\-p, \-\-port " port[:port]
 Set the TCP port (range) used by the client to listen.
@@ -106,6 +110,14 @@ option if set, or by the file extension (.mp4 or .mkv).
 .BI "\-\-record\-format " format
 Force recording format (either mp4 or mkv).
 
+.TP
+.BI "\-\-render\-driver " name
+Request SDL to use the given render driver (this is just a hint).
+
+Supported names are currently "direct3d", "opengl", "opengles2", "opengles", "metal" and "software".
+.UR https://wiki.libsdl.org/SDL_HINT_RENDER_DRIVER
+.UE
+
 .TP
 .B \-\-render\-expired\-frames
 By default, to minimize latency, scrcpy always renders the last available decoded frame, and drops any previous ones. This flag forces to render all frames, at a cost of a possible increased latency.

app/src/cli.c

@@ -75,6 +75,11 @@ scrcpy_print_usage(const char *arg0) {
         "        Do not display device (only when screen recording is\n"
         "        enabled).\n"
         "\n"
+        "    --no-mipmaps\n"
+        "        If the renderer is OpenGL 3.0+ or OpenGL ES 2.0+, then\n"
+        "        mipmaps are automatically generated to improve downscaling\n"
+        "        quality. This option disables the generation of mipmaps.\n"
+        "\n"
         "    -p, --port port[:port]\n"
         "        Set the TCP port (range) used by the client to listen.\n"
         "        Default is %d:%d.\n"
@@ -99,6 +104,13 @@ scrcpy_print_usage(const char *arg0) {
         "    --record-format format\n"
         "        Force recording format (either mp4 or mkv).\n"
         "\n"
+        "    --render-driver name\n"
+        "        Request SDL to use the given render driver (this is just a\n"
+        "        hint).\n"
+        "        Supported names are currently \"direct3d\", \"opengl\",\n"
+        "        \"opengles2\", \"opengles\", \"metal\" and \"software\".\n"
+        "        <https://wiki.libsdl.org/SDL_HINT_RENDER_DRIVER>\n"
+        "\n"
         "    --render-expired-frames\n"
         "        By default, to minimize latency, scrcpy always renders the\n"
         "        last available decoded frame, and drops any previous ones.\n"
@@ -454,6 +466,8 @@ guess_record_format(const char *filename) {
 #define OPT_LOCK_VIDEO_ORIENTATION 1013
 #define OPT_DISPLAY_ID             1014
 #define OPT_ROTATION               1015
+#define OPT_RENDER_DRIVER          1016
+#define OPT_NO_MIPMAPS             1017
 
 bool
 scrcpy_parse_args(struct scrcpy_cli_args *args, int argc, char *argv[]) {
@@ -470,10 +484,12 @@ scrcpy_parse_args(struct scrcpy_cli_args *args, int argc, char *argv[]) {
         {"max-size",               required_argument, NULL, 'm'},
         {"no-control",             no_argument,       NULL, 'n'},
         {"no-display",             no_argument,       NULL, 'N'},
+        {"no-mipmaps",             no_argument,       NULL, OPT_NO_MIPMAPS},
         {"port",                   required_argument, NULL, 'p'},
         {"push-target",            required_argument, NULL, OPT_PUSH_TARGET},
         {"record",                 required_argument, NULL, 'r'},
         {"record-format",          required_argument, NULL, OPT_RECORD_FORMAT},
+        {"render-driver",          required_argument, NULL, OPT_RENDER_DRIVER},
         {"render-expired-frames",  no_argument,       NULL,
                                                   OPT_RENDER_EXPIRED_FRAMES},
         {"rotation",               required_argument, NULL, OPT_ROTATION},
@@ -617,6 +633,12 @@ scrcpy_parse_args(struct scrcpy_cli_args *args, int argc, char *argv[]) {
                     return false;
                 }
                 break;
+            case OPT_RENDER_DRIVER:
+                opts->render_driver = optarg;
+                break;
+            case OPT_NO_MIPMAPS:
+                opts->mipmaps = false;
+                break;
             default:
                 // getopt prints the error message on stderr
                 return false;

app/src/opengl.c

@@ -0,0 +1,56 @@
+#include "opengl.h"
+
+#include <assert.h>
+#include <stdio.h>
+#include "SDL2/SDL.h"
+
+void
+sc_opengl_init(struct sc_opengl *gl) {
+    gl->GetString = SDL_GL_GetProcAddress("glGetString");
+    assert(gl->GetString);
+
+    gl->TexParameterf = SDL_GL_GetProcAddress("glTexParameterf");
+    assert(gl->TexParameterf);
+
+    gl->TexParameteri = SDL_GL_GetProcAddress("glTexParameteri");
+    assert(gl->TexParameteri);
+
+    // optional
+    gl->GenerateMipmap = SDL_GL_GetProcAddress("glGenerateMipmap");
+
+    const char *version = (const char *) gl->GetString(GL_VERSION);
+    assert(version);
+    gl->version = version;
+
+#define OPENGL_ES_PREFIX "OpenGL ES "
+    /* starts with "OpenGL ES " */
+    gl->is_opengles = !strncmp(gl->version, OPENGL_ES_PREFIX,
+                               sizeof(OPENGL_ES_PREFIX) - 1);
+    if (gl->is_opengles) {
+        /* skip the prefix */
+        version += sizeof(PREFIX) - 1;
+    }
+
+    int r = sscanf(version, "%d.%d", &gl->version_major, &gl->version_minor);
+    if (r != 2) {
+        // failed to parse the version
+        gl->version_major = 0;
+        gl->version_minor = 0;
+    }
+}
+
+bool
+sc_opengl_version_at_least(struct sc_opengl *gl,
+                           int minver_major, int minver_minor,
+                           int minver_es_major, int minver_es_minor)
+{
+    if (gl->is_opengles) {
+        return gl->version_major > minver_es_major
+            || (gl->version_major == minver_es_major
+             && gl->version_minor >= minver_es_minor);
+    }
+
+    return gl->version_major > minver_major
+        || (gl->version_major == minver_major
+         && gl->version_minor >= minver_minor);
+}

app/src/opengl.h

@@ -0,0 +1,36 @@
+#ifndef SC_OPENGL_H
+#define SC_OPENGL_H
+
+#include <stdbool.h>
+#include <SDL2/SDL_opengl.h>
+
+#include "config.h"
+
+struct sc_opengl {
+    const char *version;
+    bool is_opengles;
+    int version_major;
+    int version_minor;
+
+    const GLubyte *
+    (*GetString)(GLenum name);
+
+    void
+    (*TexParameterf)(GLenum target, GLenum pname, GLfloat param);
+
+    void
+    (*TexParameteri)(GLenum target, GLenum pname, GLint param);
+
+    void
+    (*GenerateMipmap)(GLenum target);
+};
+
+void
+sc_opengl_init(struct sc_opengl *gl);
+
+bool
+sc_opengl_version_at_least(struct sc_opengl *gl,
+                           int minver_major, int minver_minor,
+                           int minver_es_major, int minver_es_minor);
+
+#endif

app/src/scrcpy.c

@@ -47,7 +47,7 @@ static struct input_manager input_manager = {
 
 // init SDL and set appropriate hints
 static bool
-sdl_init_and_configure(bool display) {
+sdl_init_and_configure(bool display, const char *render_driver) {
     uint32_t flags = display ? SDL_INIT_VIDEO : SDL_INIT_EVENTS;
     if (SDL_Init(flags)) {
         LOGC("Could not initialize SDL: %s", SDL_GetError());
@@ -60,6 +60,10 @@ sdl_init_and_configure(bool display) {
         return true;
     }
 
+    if (render_driver && !SDL_SetHint(SDL_HINT_RENDER_DRIVER, render_driver)) {
+        LOGW("Could not set render driver");
+    }
+
     // Linear filtering
     if (!SDL_SetHint(SDL_HINT_RENDER_SCALE_QUALITY, "1")) {
         LOGW("Could not enable linear filtering");
@@ -310,7 +314,7 @@ scrcpy(const struct scrcpy_options *options) {
     bool controller_initialized = false;
     bool controller_started = false;
 
-    if (!sdl_init_and_configure(options->display)) {
+    if (!sdl_init_and_configure(options->display, options->render_driver)) {
         goto end;
     }
 
@@ -397,7 +401,7 @@ scrcpy(const struct scrcpy_options *options) {
                                    options->window_y, options->window_width,
                                    options->window_height,
                                    options->window_borderless,
-                                   options->rotation)) {
+                                   options->rotation, options-> mipmaps)) {
             goto end;
         }
 

app/src/scrcpy.h

@@ -15,6 +15,7 @@ struct scrcpy_options {
     const char *record_filename;
     const char *window_title;
     const char *push_target;
+    const char *render_driver;
     enum recorder_format record_format;
     struct port_range port_range;
     uint16_t max_size;
@@ -36,6 +37,7 @@ struct scrcpy_options {
     bool render_expired_frames;
     bool prefer_text;
     bool window_borderless;
+    bool mipmaps;
 };
 
 #define SCRCPY_OPTIONS_DEFAULT { \
@@ -44,6 +46,7 @@ struct scrcpy_options {
     .record_filename = NULL, \
     .window_title = NULL, \
     .push_target = NULL, \
+    .render_driver = NULL, \
     .record_format = RECORDER_FORMAT_AUTO, \
     .port_range = { \
         .first = DEFAULT_LOCAL_PORT_RANGE_FIRST, \
@@ -68,6 +71,7 @@ struct scrcpy_options {
     .render_expired_frames = false, \
     .prefer_text = false, \
     .window_borderless = false, \
+    .mipmaps = true, \
 }
 
 bool

app/src/screen.c

@@ -168,10 +168,30 @@ screen_init(struct screen *screen) {
 }
 
 static inline SDL_Texture *
-create_texture(SDL_Renderer *renderer, struct size frame_size) {
+create_texture(struct screen *screen) {
-    return SDL_CreateTexture(renderer, SDL_PIXELFORMAT_YV12,
+    SDL_Renderer *renderer = screen->renderer;
+    struct size size = screen->frame_size;
+    SDL_Texture *texture = SDL_CreateTexture(renderer, SDL_PIXELFORMAT_YV12,
                                              SDL_TEXTUREACCESS_STREAMING,
-                             frame_size.width, frame_size.height);
+                                             size.width, size.height);
+    if (!texture) {
+        return NULL;
+    }
+
+    if (screen->mipmaps) {
+        struct sc_opengl *gl = &screen->gl;
+
+        SDL_GL_BindTexture(texture, NULL, NULL);
+
+        // Enable trilinear filtering for downscaling
+        gl->TexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER,
+                          GL_LINEAR_MIPMAP_LINEAR);
+        gl->TexParameterf(GL_TEXTURE_2D, GL_TEXTURE_LOD_BIAS, -.5f);
+
+        SDL_GL_UnbindTexture(texture);
+    }
+
+    return texture;
 }
 
 bool
@@ -179,7 +199,7 @@ screen_init_rendering(struct screen *screen, const char *window_title,
                       struct size frame_size, bool always_on_top,
                       int16_t window_x, int16_t window_y, uint16_t window_width,
                       uint16_t window_height, bool window_borderless,
-                      uint8_t rotation) {
+                      uint8_t rotation, bool mipmaps) {
     screen->frame_size = frame_size;
     screen->rotation = rotation;
     if (rotation) {
@@ -226,6 +246,11 @@ screen_init_rendering(struct screen *screen, const char *window_title,
         return false;
     }
 
+    SDL_RendererInfo renderer_info;
+    int r = SDL_GetRendererInfo(screen->renderer, &renderer_info);
+    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());
@@ -233,6 +258,32 @@ screen_init_rendering(struct screen *screen, const char *window_title,
         return false;
     }
 
+    // stats with "opengl"
+    screen->use_opengl = renderer_name && !strncmp(renderer_name, "opengl", 6);
+    if (screen->use_opengl) {
+        struct sc_opengl *gl = &screen->gl;
+        sc_opengl_init(gl);
+
+        LOGI("OpenGL version: %s", gl->version);
+
+        if (mipmaps) {
+            bool supports_mipmaps =
+                sc_opengl_version_at_least(gl, 3, 0, /* OpenGL 3.0+ */
+                                               2, 0  /* OpenGL ES 2.0+ */);
+            if (supports_mipmaps) {
+                LOGI("Trilinear filtering enabled");
+                screen->mipmaps = true;
+            } else {
+                LOGW("Trilinear filtering disabled "
+                     "(OpenGL 3.0+ or ES 2.0+ required)");
+            }
+        } else {
+            LOGI("Trilinear filtering disabled");
+        }
+    } else {
+        LOGW("Trilinear filtering disabled (not an OpenGL renderer)");
+    }
+
     SDL_Surface *icon = read_xpm(icon_xpm);
     if (icon) {
         SDL_SetWindowIcon(screen->window, icon);
@@ -243,7 +294,7 @@ screen_init_rendering(struct screen *screen, const char *window_title,
 
     LOGI("Initial texture: %" PRIu16 "x%" PRIu16, frame_size.width,
                                                   frame_size.height);
-    screen->texture = create_texture(screen->renderer, frame_size);
+    screen->texture = create_texture(screen);
     if (!screen->texture) {
         LOGC("Could not create texture: %s", SDL_GetError());
         screen_destroy(screen);
@@ -341,7 +392,7 @@ prepare_for_frame(struct screen *screen, struct size new_frame_size) {
 
         LOGI("New texture: %" PRIu16 "x%" PRIu16,
                      screen->frame_size.width, screen->frame_size.height);
-        screen->texture = create_texture(screen->renderer, new_frame_size);
+        screen->texture = create_texture(screen);
         if (!screen->texture) {
             LOGC("Could not create texture: %s", SDL_GetError());
             return false;
@@ -358,6 +409,13 @@ update_texture(struct screen *screen, const AVFrame *frame) {
             frame->data[0], frame->linesize[0],
             frame->data[1], frame->linesize[1],
             frame->data[2], frame->linesize[2]);
+
+    if (screen->mipmaps) {
+        assert(screen->use_opengl);
+        SDL_GL_BindTexture(screen->texture, NULL, NULL);
+        screen->gl.GenerateMipmap(GL_TEXTURE_2D);
+        SDL_GL_UnbindTexture(screen->texture);
+    }
 }
 
 bool

app/src/screen.h

@@ -7,6 +7,7 @@
 
 #include "config.h"
 #include "common.h"
+#include "opengl.h"
 
 #define WINDOW_POSITION_UNDEFINED (-0x8000)
 
@@ -16,6 +17,8 @@ struct screen {
     SDL_Window *window;
     SDL_Renderer *renderer;
     SDL_Texture *texture;
+    bool use_opengl;
+    struct sc_opengl gl;
     struct size frame_size;
     struct size content_size; // rotated frame_size
     // The window size the last time it was not maximized or fullscreen.
@@ -29,12 +32,15 @@ struct screen {
     bool fullscreen;
     bool maximized;
     bool no_window;
+    bool mipmaps;
 };
 
 #define SCREEN_INITIALIZER { \
     .window = NULL, \
     .renderer = NULL, \
     .texture = NULL, \
+    .use_opengl = false, \
+    .gl = {0}, \
     .frame_size = { \
         .width = 0, \
         .height = 0, \
@@ -56,6 +62,7 @@ struct screen {
     .fullscreen = false, \
     .maximized = false, \
     .no_window = false, \
+    .mipmaps = false, \
 }
 
 // initialize default values
@@ -69,7 +76,7 @@ screen_init_rendering(struct screen *screen, const char *window_title,
                       struct size frame_size, bool always_on_top,
                       int16_t window_x, int16_t window_y, uint16_t window_width,
                       uint16_t window_height, bool window_borderless,
-                      uint8_t rotation);
+                      uint8_t rotation, bool mipmaps);
 
 // show the window
 void