From 5532cbf53e66e3a1ca86e6ab7c5d488254900c82 Mon Sep 17 00:00:00 2001
From: klemek <klemek.dev@proton.me>
Date: Mon, 10 Nov 2025 16:29:11 +0100
Subject: [PATCH] chore: reduce debt with const values

---
 src/config_file.c |  2 +-
 src/config_file.h |  2 +-
 src/file.c        | 13 ++++++-------
 src/file.h        | 10 +++++-----
 src/forge.c       |  8 ++++----
 src/forge.h       |  2 +-
 src/midi.c        |  6 ++++--
 src/midi.h        |  6 ++++--
 src/project.c     |  5 +++--
 src/project.h     |  5 +++--
 src/shaders.c     | 48 +++++++++++++++++++++++++++--------------------
 src/shaders.h     | 15 ++++++++-------
 src/state.c       | 44 +++++++++++++++++++++++--------------------
 src/state.h       | 23 ++++++++++++-----------
 src/tempo.c       |  8 ++++----
 src/tempo.h       |  4 ++--
 src/video.c       |  8 ++++----
 src/video.h       |  4 ++--
 src/window.c      |  8 ++++----
 src/window.h      |  6 +++---
 20 files changed, 123 insertions(+), 104 deletions(-)

diff --git a/src/config_file.c b/src/config_file.c
index eef247f..0e773ec 100644
--- a/src/config_file.c
+++ b/src/config_file.c
@@ -64,7 +64,7 @@ static void parse_config_file_line(const ConfigFile *config, char *line) {
   hashmap_set(config->map, &item);
 }
 
-void config_file_read(ConfigFile *config, char *path) {
+void config_file_read(ConfigFile *config, const char *path) {
   File file;
   char *line;
   char *rest;
diff --git a/src/config_file.h b/src/config_file.h
index b14226c..d4ad7a1 100644
--- a/src/config_file.h
+++ b/src/config_file.h
@@ -3,7 +3,7 @@
 #ifndef CONFIG_FILE_H
 #define CONFIG_FILE_H
 
-void config_file_read(ConfigFile *config, char *path);
+void config_file_read(ConfigFile *config, const char *path);
 
 const char *config_file_get_str(const ConfigFile *config, const char *key,
                                 const char *default_value);
diff --git a/src/file.c b/src/file.c
index adce0ee..16c536e 100644
--- a/src/file.c
+++ b/src/file.c
@@ -12,7 +12,7 @@
 #include "file.h"
 #include "string.h"
 
-static time_t get_file_time(File *file) {
+static time_t get_file_time(const File *file) {
   struct stat attr;
 
   if (stat(file->path, &attr) == 0) {
@@ -22,7 +22,7 @@ static time_t get_file_time(File *file) {
   return 0;
 }
 
-bool file_should_update(File *file) {
+bool file_should_update(const File *file) {
   return file->last_write != get_file_time(file);
 }
 
@@ -70,7 +70,7 @@ bool file_update(File *file) {
   return true;
 }
 
-void file_read(File *file, char *path) {
+void file_read(File *file, const char *path) {
   strlcpy(file->path, path, STR_LEN);
   file->content = NULL;
   file->error = false;
@@ -79,7 +79,7 @@ void file_read(File *file, char *path) {
   file_update(file);
 }
 
-void file_dump(char *path, char *content) {
+void file_dump(const char *path, const char *content) {
   FILE *file_pointer;
 
   log_info("Dumping %s...", path);
@@ -98,7 +98,7 @@ void file_dump(char *path, char *content) {
   fclose(file_pointer);
 }
 
-void file_write(char *path, StringArray *lines) {
+void file_write(const char *path, const StringArray *lines) {
   FILE *file_pointer;
 
   log_info("Writing %s...", path);
@@ -119,9 +119,8 @@ void file_write(char *path, StringArray *lines) {
   fclose(file_pointer);
 }
 
-void file_free(File *file) {
+void file_free(const File *file) {
   if (!file->error) {
     free(file->content);
-    file->error = true;
   }
 }
diff --git a/src/file.h b/src/file.h
index dfb7b22..59ddd72 100644
--- a/src/file.h
+++ b/src/file.h
@@ -3,16 +3,16 @@
 #ifndef FILE_H
 #define FILE_H
 
-void file_read(File *file, char *path);
+void file_read(File *file, const char *path);
 
-bool file_should_update(File *file);
+bool file_should_update(const File *file);
 
 bool file_update(File *file);
 
-void file_write(char *path, StringArray *lines);
+void file_write(const char *path, const StringArray *lines);
 
-void file_dump(char *path, char *content);
+void file_dump(const char *path, const char *content);
 
-void file_free(File *file);
+void file_free(const File *file);
 
 #endif /* FILE_H */
\ No newline at end of file
diff --git a/src/forge.c b/src/forge.c
index 2c82af0..02b2c23 100644
--- a/src/forge.c
+++ b/src/forge.c
@@ -57,7 +57,7 @@ static void compute_fps(bool trace_fps) {
   }
 }
 
-static void init_context(Parameters *params, unsigned int in_count) {
+static void init_context(const Parameters *params, unsigned int in_count) {
   state_init(context, &project.state_config, params->demo, params->auto_random,
              params->base_tempo, params->state_file, params->load_state);
 
@@ -82,7 +82,7 @@ static void reload_shader(unsigned int i) {
   shaders_update(&program, &project.fragment_shaders[i][0], i);
 }
 
-static void init_inputs(StringArray *video_in, unsigned int video_size) {
+static void init_inputs(const StringArray *video_in, unsigned int video_size) {
   inputs.length = video_in->length;
 
   for (unsigned int i = 0; i < video_in->length; i++) {
@@ -173,7 +173,7 @@ static void loop(bool hr, bool trace_fps) {
   window_events();
 }
 
-void forge_run(Parameters *params) {
+void forge_run(const Parameters *params) {
   context = shared_init_context("/" PACKAGE "_context");
 
   context->stop = false;
@@ -195,7 +195,7 @@ void forge_run(Parameters *params) {
   midi_open(&midi, config_file_get_str(&project.config, "MIDI_HW", "hw"));
 
   if (midi.error) {
-    params->demo = true;
+    context->demo = true;
   } else {
     trace_midi = params->trace_midi;
 
diff --git a/src/forge.h b/src/forge.h
index b439d9e..2472be7 100644
--- a/src/forge.h
+++ b/src/forge.h
@@ -3,6 +3,6 @@
 #ifndef FORGE_H
 #define FORGE_H
 
-void forge_run(Parameters *params);
+void forge_run(const Parameters *params);
 
 #endif /* FORGE_H */
\ No newline at end of file
diff --git a/src/midi.c b/src/midi.c
index 9473f72..a4274a7 100644
--- a/src/midi.c
+++ b/src/midi.c
@@ -19,7 +19,8 @@ void midi_open(MidiDevice *device, const char *name) {
   log_info("(%s) MIDI open", name);
 }
 
-void midi_write(MidiDevice *device, unsigned char code, unsigned char value) {
+void midi_write(const MidiDevice *device, unsigned char code,
+                unsigned char value) {
   unsigned char buffer[3];
 
   buffer[0] = 0xB0;
@@ -29,7 +30,8 @@ void midi_write(MidiDevice *device, unsigned char code, unsigned char value) {
   snd_rawmidi_write(device->output, buffer, 3);
 }
 
-bool midi_background_listen(MidiDevice *device, SharedContext *context,
+bool midi_background_listen(const MidiDevice *device,
+                            const SharedContext *context,
                             void (*event_callback)(unsigned char code,
                                                    unsigned char value)) {
   pid_t pid;
diff --git a/src/midi.h b/src/midi.h
index 8f51da4..18616c2 100644
--- a/src/midi.h
+++ b/src/midi.h
@@ -4,8 +4,10 @@
 #define MIDI_H
 
 void midi_open(MidiDevice *device, const char *name);
-void midi_write(MidiDevice *device, unsigned char code, unsigned char value);
-bool midi_background_listen(MidiDevice *device, SharedContext *context,
+void midi_write(const MidiDevice *device, unsigned char code,
+                unsigned char value);
+bool midi_background_listen(const MidiDevice *device,
+                            const SharedContext *context,
                             void (*event_callback)(unsigned char code,
                                                    unsigned char value));
 
diff --git a/src/project.c b/src/project.c
index 5e72195..69e27f5 100644
--- a/src/project.c
+++ b/src/project.c
@@ -76,7 +76,8 @@ static bool read_fragment_shader_file(Project *project, const char *frag_prefix,
   return parse_fragment_shader_file(project, i);
 }
 
-void project_init(Project *project, char *project_path, char *config_file) {
+void project_init(Project *project, const char *project_path,
+                  const char *config_file) {
   char config_path[STR_LEN];
   const char *frag_prefix;
 
@@ -134,7 +135,7 @@ void project_reload(Project *project, void (*reload_callback)(unsigned int)) {
   }
 }
 
-void project_free(Project *project) {
+void project_free(const Project *project) {
   for (unsigned int i = 0; i < project->frag_count; i++) {
     file_free(&project->fragment_shaders[i][0]);
   }
diff --git a/src/project.h b/src/project.h
index cca35a4..12fa21b 100644
--- a/src/project.h
+++ b/src/project.h
@@ -3,10 +3,11 @@
 #ifndef PROJECT_H
 #define PROJECT_H
 
-void project_init(Project *project, char *project_path, char *config_file);
+void project_init(Project *project, const char *project_path,
+                  const char *config_file);
 
 void project_reload(Project *project, void (*reload_callback)(unsigned int));
 
-void project_free(Project *project);
+void project_free(const Project *project);
 
 #endif /* PROJECT_H */
\ No newline at end of file
diff --git a/src/shaders.c b/src/shaders.c
index ea0001b..2d3e70d 100644
--- a/src/shaders.c
+++ b/src/shaders.c
@@ -35,7 +35,8 @@ static void init_gl(ShaderProgram *program) {
   gladLoadEGL(program->egl_display, glfwGetProcAddress);
 }
 
-static void init_textures(ShaderProgram *program, SharedContext *context) {
+static void init_textures(ShaderProgram *program,
+                          const SharedContext *context) {
   glGenTextures(program->tex_count, program->textures);
 
   for (unsigned int i = 0; i < program->tex_count; i++) {
@@ -110,7 +111,7 @@ static void link_input_to_texture(ShaderProgram *program, VideoCapture *input,
   log_info("Texture %d linked to %s", texture_index, input->name);
 }
 
-static void init_input(ShaderProgram *program, ConfigFile *config,
+static void init_input(ShaderProgram *program, const ConfigFile *config,
                        VideoCaptureArray *inputs) {
   unsigned int tex_i;
   char name[STR_LEN];
@@ -126,7 +127,8 @@ static void init_input(ShaderProgram *program, ConfigFile *config,
   }
 }
 
-static void init_framebuffers(ShaderProgram *program, ConfigFile *config) {
+static void init_framebuffers(ShaderProgram *program,
+                              const ConfigFile *config) {
   unsigned int tex_i;
   char name[STR_LEN];
 
@@ -182,7 +184,8 @@ static void bind_vertices(ShaderProgram *program, unsigned int index) {
   }
 }
 
-static bool compile_shader(GLuint shader_id, char *name, char *source_code) {
+static bool compile_shader(GLuint shader_id, const char *name,
+                           const char *source_code) {
   GLint status_params;
   char log[STR_LEN];
 
@@ -208,7 +211,7 @@ static bool compile_shader(GLuint shader_id, char *name, char *source_code) {
   return status_params == GL_TRUE;
 }
 
-static void init_shaders(ShaderProgram *program, Project *project) {
+static void init_shaders(ShaderProgram *program, const Project *project) {
   // compile vertex shader
   program->vertex_shader = glCreateShader(GL_VERTEX_SHADER);
   program->error |= !compile_shader(
@@ -228,7 +231,8 @@ static void init_shaders(ShaderProgram *program, Project *project) {
 }
 
 static void init_single_program(ShaderProgram *program, unsigned int i,
-                                ConfigFile *config, StateConfig *state_config) {
+                                const ConfigFile *config,
+                                const StateConfig *state_config) {
   unsigned int index1;
   unsigned int index2;
   char name[STR_LEN];
@@ -365,15 +369,15 @@ static void init_single_program(ShaderProgram *program, unsigned int i,
   log_info("Program %d initialized", i + 1);
 }
 
-static void init_programs(ShaderProgram *program, ConfigFile *config,
-                          StateConfig *state_config) {
+static void init_programs(ShaderProgram *program, const ConfigFile *config,
+                          const StateConfig *state_config) {
   for (unsigned int i = 0; i < program->frag_count; i++) {
     init_single_program(program, i, config, state_config);
   }
 }
 
-void shaders_init(ShaderProgram *program, Project *project,
-                  SharedContext *context, VideoCaptureArray *inputs,
+void shaders_init(ShaderProgram *program, const Project *project,
+                  const SharedContext *context, VideoCaptureArray *inputs,
                   bool rebind) {
   if (!rebind) {
     program->error = false;
@@ -418,7 +422,7 @@ void shaders_init(ShaderProgram *program, Project *project,
   ;
 }
 
-void shaders_update(ShaderProgram *program, File *fragment_shader,
+void shaders_update(ShaderProgram *program, const File *fragment_shader,
                     unsigned int i) {
   bool result;
 
@@ -432,7 +436,8 @@ void shaders_update(ShaderProgram *program, File *fragment_shader,
   }
 }
 
-static void update_viewport(ShaderProgram *program, SharedContext *context) {
+static void update_viewport(ShaderProgram *program,
+                            const SharedContext *context) {
   // viewport changed
   if (context->resolution[0] != program->last_resolution[0] ||
       context->resolution[1] != program->last_resolution[1]) {
@@ -442,6 +447,8 @@ static void update_viewport(ShaderProgram *program, SharedContext *context) {
       glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, context->tex_resolution[0],
                    context->tex_resolution[1], 0, GL_RGB, GL_UNSIGNED_BYTE, 0);
     }
+    program->last_resolution[0] = context->resolution[0];
+    program->last_resolution[1] = context->resolution[1];
   }
 }
 
@@ -457,21 +464,21 @@ static void write_uniform_1i(GLuint location, unsigned int value) {
   }
 }
 
-static void write_uniform_2f(GLuint location, vec2 *value) {
+static void write_uniform_2f(GLuint location, const vec2 *value) {
   if (location != unused_uniform) {
     glUniform2fv(location, 1, (const GLfloat *)value);
   }
 }
 
 static void write_uniform_multi_3f(GLuint location, unsigned int count,
-                                   vec3 *value) {
+                                   const vec3 *value) {
   if (location != unused_uniform) {
     glUniform3fv(location, count, (const GLfloat *)value);
   }
 }
 
-static void use_program(ShaderProgram *program, int i, bool output,
-                        SharedContext *context) {
+static void use_program(const ShaderProgram *program, int i, bool output,
+                        const SharedContext *context) {
   unsigned int k;
   unsigned int offset;
   unsigned int subcount;
@@ -569,7 +576,7 @@ static void use_program(ShaderProgram *program, int i, bool output,
   glDrawArrays(GL_TRIANGLES, 0, 6);
 }
 
-void shaders_compute(ShaderProgram *program, SharedContext *context,
+void shaders_compute(ShaderProgram *program, const SharedContext *context,
                      bool monitor, bool output_only) {
   if (!output_only) {
     glBindVertexArray(program->vertex_array[0]);
@@ -593,7 +600,7 @@ void shaders_compute(ShaderProgram *program, SharedContext *context,
               true, context);
 }
 
-void shaders_free(ShaderProgram *program) {
+void shaders_free(const ShaderProgram *program) {
   for (unsigned int i = 0; i < program->frag_count; i++) {
     glDeleteProgram(program->programs[i]);
   }
@@ -603,11 +610,12 @@ void shaders_free(ShaderProgram *program) {
   glDeleteBuffers(1, &program->vertex_buffer);
 }
 
-void shaders_free_window(ShaderProgram *program, bool secondary) {
+void shaders_free_window(const ShaderProgram *program, bool secondary) {
   glDeleteVertexArrays(1, &program->vertex_array[secondary ? 1 : 0]);
 }
 
-void shaders_free_input(ShaderProgram *program, VideoCapture *input) {
+void shaders_free_input(const ShaderProgram *program,
+                        const VideoCapture *input) {
   if (!input->error && input->dma_image != EGL_NO_IMAGE_KHR) {
     eglDestroyImageKHR(program->egl_display, input->dma_image);
   }
diff --git a/src/shaders.h b/src/shaders.h
index 317b460..68d4a97 100644
--- a/src/shaders.h
+++ b/src/shaders.h
@@ -3,20 +3,21 @@
 #ifndef SHADERS_H
 #define SHADERS_H
 
-void shaders_init(ShaderProgram *program, Project *project,
-                  SharedContext *context, VideoCaptureArray *inputs,
+void shaders_init(ShaderProgram *program, const Project *project,
+                  const SharedContext *context, VideoCaptureArray *inputs,
                   bool rebind);
 
-void shaders_update(ShaderProgram *program, File *fragment_shader,
+void shaders_update(ShaderProgram *program, const File *fragment_shader,
                     unsigned int i);
 
-void shaders_compute(ShaderProgram *program, SharedContext *context,
+void shaders_compute(ShaderProgram *program, const SharedContext *context,
                      bool monitor, bool output_only);
 
-void shaders_free(ShaderProgram *program);
+void shaders_free(const ShaderProgram *program);
 
-void shaders_free_window(ShaderProgram *program, bool secondary);
+void shaders_free_window(const ShaderProgram *program, bool secondary);
 
-void shaders_free_input(ShaderProgram *program, VideoCapture *input);
+void shaders_free_input(const ShaderProgram *program,
+                        const VideoCapture *input);
 
 #endif /* SHADERS_H */
\ No newline at end of file
diff --git a/src/state.c b/src/state.c
index fe7f273..ba332be 100644
--- a/src/state.c
+++ b/src/state.c
@@ -12,7 +12,7 @@
 #include "state.h"
 #include "tempo.h"
 
-void state_parse_config(StateConfig *state_config, ConfigFile *config) {
+void state_parse_config(StateConfig *state_config, const ConfigFile *config) {
   unsigned int offset;
   unsigned int count;
   char name[STR_LEN];
@@ -118,15 +118,16 @@ void state_parse_config(StateConfig *state_config, ConfigFile *config) {
       config_file_get_int(config, "TAP_TEMPO", UNSET_MIDI_CODE);
 }
 
-static void safe_midi_write(MidiDevice *midi, unsigned int code,
+static void safe_midi_write(const MidiDevice *midi, unsigned int code,
                             unsigned char value) {
   if (code != UNSET_MIDI_CODE) {
     midi_write(midi, code, value);
   }
 }
 
-static void update_page(SharedContext *context, StateConfig *state_config,
-                        MidiDevice *midi) {
+static void update_page(const SharedContext *context,
+                        const StateConfig *state_config,
+                        const MidiDevice *midi) {
   unsigned int page_item_min;
   unsigned int page_item_max;
   // SHOW PAGE
@@ -155,8 +156,9 @@ static void update_page(SharedContext *context, StateConfig *state_config,
   }
 }
 
-static void update_active(SharedContext *context, StateConfig *state_config,
-                          MidiDevice *midi) {
+static void update_active(const SharedContext *context,
+                          const StateConfig *state_config,
+                          const MidiDevice *midi) {
   unsigned int k;
 
   for (unsigned int i = 0; i < state_config->midi_active_counts.length; i++) {
@@ -169,8 +171,9 @@ static void update_active(SharedContext *context, StateConfig *state_config,
   }
 }
 
-static void update_values(SharedContext *context, StateConfig *state_config,
-                          MidiDevice *midi) {
+static void update_values(const SharedContext *context,
+                          const StateConfig *state_config,
+                          const MidiDevice *midi) {
   unsigned int j;
   unsigned int k;
   unsigned int part;
@@ -185,8 +188,8 @@ static void update_values(SharedContext *context, StateConfig *state_config,
   }
 }
 
-void state_apply_event(SharedContext *context, StateConfig *state_config,
-                       MidiDevice *midi, unsigned char code,
+void state_apply_event(SharedContext *context, const StateConfig *state_config,
+                       const MidiDevice *midi, unsigned char code,
                        unsigned char value, bool trace_midi) {
   unsigned int i, j, k, part;
   bool found;
@@ -276,8 +279,9 @@ void state_apply_event(SharedContext *context, StateConfig *state_config,
   }
 }
 
-bool state_background_write(SharedContext *context, StateConfig *state_config,
-                            MidiDevice *midi) {
+bool state_background_write(SharedContext *context,
+                            const StateConfig *state_config,
+                            const MidiDevice *midi) {
   pid_t pid;
   bool beat_active, last_active, change, last_change;
 
@@ -327,8 +331,8 @@ bool state_background_write(SharedContext *context, StateConfig *state_config,
   return false;
 }
 
-static void state_load(SharedContext *context, StateConfig *state_config,
-                       char *state_file) {
+static void state_load(SharedContext *context, const StateConfig *state_config,
+                       const char *state_file) {
   ConfigFile saved_state;
   char key[STR_LEN];
 
@@ -367,9 +371,9 @@ static void state_load(SharedContext *context, StateConfig *state_config,
   config_file_free(&saved_state);
 }
 
-void state_init(SharedContext *context, StateConfig *state_config, bool demo,
-                bool auto_random, unsigned int base_tempo, char *state_file,
-                bool load_state) {
+void state_init(SharedContext *context, const StateConfig *state_config,
+                bool demo, bool auto_random, unsigned int base_tempo,
+                const char *state_file, bool load_state) {
   tempo_init(&context->tempo);
   tempo_set(&context->tempo, base_tempo);
   context->demo = demo;
@@ -399,14 +403,14 @@ void state_init(SharedContext *context, StateConfig *state_config, bool demo,
   }
 }
 
-void state_randomize(SharedContext *context, StateConfig *state_config) {
+void state_randomize(SharedContext *context, const StateConfig *state_config) {
   for (unsigned int i = 0; i < context->state.length; i++) {
     context->state.values[i] = rand_uint(state_config->state_max);
   }
 }
 
-void state_save(SharedContext *context, StateConfig *state_config,
-                char *state_file) {
+void state_save(const SharedContext *context, const StateConfig *state_config,
+                const char *state_file) {
   StringArray lines;
 
   log_info("Saving state to '%s'...", state_file);
diff --git a/src/state.h b/src/state.h
index 9e4adde..b21258d 100644
--- a/src/state.h
+++ b/src/state.h
@@ -3,22 +3,23 @@
 #ifndef STATE_H
 #define STATE_H
 
-void state_parse_config(StateConfig *state_config, ConfigFile *config);
+void state_parse_config(StateConfig *state_config, const ConfigFile *config);
 
-void state_apply_event(SharedContext *context, StateConfig *state_config,
-                       MidiDevice *midi, unsigned char code,
+void state_apply_event(SharedContext *context, const StateConfig *state_config,
+                       const MidiDevice *midi, unsigned char code,
                        unsigned char value, bool trace_midi);
 
-bool state_background_write(SharedContext *context, StateConfig *state_config,
-                            MidiDevice *midi);
+bool state_background_write(SharedContext *context,
+                            const StateConfig *state_config,
+                            const MidiDevice *midi);
 
-void state_init(SharedContext *context, StateConfig *state_config, bool demo,
-                bool auto_random, unsigned int base_tempo, char *state_file,
-                bool load_state);
+void state_init(SharedContext *context, const StateConfig *state_config,
+                bool demo, bool auto_random, unsigned int base_tempo,
+                const char *state_file, bool load_state);
 
-void state_randomize(SharedContext *context, StateConfig *state_config);
+void state_randomize(SharedContext *context, const StateConfig *state_config);
 
-void state_save(SharedContext *context, StateConfig *state_config,
-                char *state_file);
+void state_save(const SharedContext *context, const StateConfig *state_config,
+                const char *state_file);
 
 #endif /* STATE_H */
\ No newline at end of file
diff --git a/src/tempo.c b/src/tempo.c
index 0fb85c1..c7418e0 100644
--- a/src/tempo.c
+++ b/src/tempo.c
@@ -33,12 +33,12 @@ void tempo_init(Tempo *tempo) {
   reset_tap_chain(tempo, t);
 }
 
-static bool is_chain_active(Tempo tempo, long t) {
+static bool is_chain_active(const Tempo tempo, long t) {
   return (tempo.last_tap + MAX_BEAT_LENGTH) > t &&
          (tempo.last_tap + (tempo.beat_length * BEATS_UNTIL_CHAIN_RESET)) > t;
 }
 
-static long get_average_tap_duration(Tempo tempo) {
+static long get_average_tap_duration(const Tempo tempo) {
   unsigned int amount;
   long running_total;
   long average_tap_duration;
@@ -115,7 +115,7 @@ void tempo_tap(Tempo *tempo) {
   add_tap_to_chain(tempo, t);
 }
 
-double tempo_total(Tempo *tempo) {
+double tempo_total(const Tempo *tempo) {
   long t;
 
   t = now();
@@ -123,6 +123,6 @@ double tempo_total(Tempo *tempo) {
   return (double)(t - tempo->last_reset) / (double)tempo->beat_length;
 }
 
-double tempo_progress(Tempo *tempo, double modulo) {
+double tempo_progress(const Tempo *tempo, double modulo) {
   return fmod(tempo_total(tempo), modulo);
 }
\ No newline at end of file
diff --git a/src/tempo.h b/src/tempo.h
index 3deb68e..932cbc3 100644
--- a/src/tempo.h
+++ b/src/tempo.h
@@ -9,8 +9,8 @@ void tempo_tap(Tempo *tempo);
 
 void tempo_set(Tempo *tempo, float value);
 
-double tempo_total(Tempo *tempo);
+double tempo_total(const Tempo *tempo);
 
-double tempo_progress(Tempo *tempo, double modulo);
+double tempo_progress(const Tempo *tempo, double modulo);
 
 #endif /* TEMPO_H */
\ No newline at end of file
diff --git a/src/video.c b/src/video.c
index 1399039..61bf5b1 100644
--- a/src/video.c
+++ b/src/video.c
@@ -66,7 +66,7 @@ static void ioctl_error(VideoCapture *video_capture, const char *operation,
   video_capture->error = true;
 }
 
-static void open_device(VideoCapture *video_capture, char *name) {
+static void open_device(VideoCapture *video_capture, const char *name) {
   strlcpy(video_capture->name, name, STR_LEN);
   video_capture->error = false;
   video_capture->fd = -1;
@@ -266,11 +266,11 @@ static void create_image_buffer(VideoCapture *video_capture) {
   ioctl(video_capture->fd, VIDIOC_QBUF, &video_capture->buf);
 }
 
-static void close_stream(VideoCapture *video_capture) {
+static void close_stream(const VideoCapture *video_capture) {
   ioctl(video_capture->fd, VIDIOC_STREAMOFF, &buf_type);
 }
 
-void video_init(VideoCapture *video_capture, char *name,
+void video_init(VideoCapture *video_capture, const char *name,
                 unsigned int preferred_height) {
   open_device(video_capture, name);
 
@@ -363,7 +363,7 @@ bool video_background_read(VideoCapture *video_capture, SharedContext *context,
   return false;
 }
 
-void video_free(VideoCapture *video_capture) {
+void video_free(const VideoCapture *video_capture) {
   if (!video_capture->error) {
     close_stream(video_capture);
   }
diff --git a/src/video.h b/src/video.h
index 6840fd9..227e41c 100644
--- a/src/video.h
+++ b/src/video.h
@@ -3,12 +3,12 @@
 #ifndef VIDEO_H
 #define VIDEO_H
 
-void video_init(VideoCapture *video_capture, char *name,
+void video_init(VideoCapture *video_capture, const char *name,
                 unsigned int preferred_height);
 
 bool video_background_read(VideoCapture *video_capture, SharedContext *context,
                            int input_index, bool trace_fps);
 
-void video_free(VideoCapture *video_capture);
+void video_free(const VideoCapture *video_capture);
 
 #endif /* VIDEO_H */
\ No newline at end of file
diff --git a/src/window.c b/src/window.c
index cfc2499..8598033 100644
--- a/src/window.c
+++ b/src/window.c
@@ -44,7 +44,7 @@ static GLFWmonitor *get_monitor(unsigned char monitor_index) {
 }
 
 static GLFWwindow *
-create_window(GLFWmonitor *monitor, char *title, Window *shared_context,
+create_window(GLFWmonitor *monitor, const char *title, Window *shared_context,
               void (*key_callback)(Window *, int, int, int, int)) {
   GLFWwindow *window;
 
@@ -92,8 +92,8 @@ void window_terminate() {
   glfwTerminate();
 }
 
-Window *window_init(char *title, unsigned char monitor_index, bool windowed,
-                    Window *shared_context,
+Window *window_init(const char *title, unsigned char monitor_index,
+                    bool windowed, Window *shared_context,
                     void (*key_callback)(Window *, int, int, int, int)) {
   GLFWwindow *window;
   GLFWmonitor *monitor;
@@ -107,7 +107,7 @@ Window *window_init(char *title, unsigned char monitor_index, bool windowed,
   return window;
 }
 
-void window_update_title(Window *window, char *title) {
+void window_update_title(Window *window, const char *title) {
   glfwSetWindowTitle(window, title);
 }
 
diff --git a/src/window.h b/src/window.h
index 4f64740..8ac12ed 100644
--- a/src/window.h
+++ b/src/window.h
@@ -7,11 +7,11 @@ void window_startup(void (*error_callback)(int, const char *));
 
 void window_terminate();
 
-Window *window_init(char *title, unsigned char monitor_index, bool windowed,
-                    Window *shared_context,
+Window *window_init(const char *title, unsigned char monitor_index,
+                    bool windowed, Window *shared_context,
                     void (*key_callback)(Window *, int, int, int, int));
 
-void window_update_title(Window *window, char *title);
+void window_update_title(Window *window, const char *title);
 
 double window_get_time();