shader: introduce shader_active_uniforms()

The existing shader api only supports caller-provided uniforms
and attributes at instantiation time, with no ability to
introspect what uniforms are actually actively present in a given
shader.

This commit adds introspection of the active uniforms for a given
shader at creation time, as well as when reloaded, keeping the
information around to be accessed via shader_active_uniforms().

The immediate impetus for this is supporting runtime discovery of
uniforms present in the shader source, with the intention of
exposing these as sequencer tracks for external manipulation.

3 files changed, 80 insertions, 12 deletions

diff --git a/src/pig.c b/src/pig.c
index 6c11c67..6161b8d 100644
--- a/src/pig.c
+++ b/src/pig.c
@@ -72,10 +72,12 @@ static void randomize_color(v3f_t *color)
 
 static void pig_uniforms_func(shader_t *shader, void *uniforms_ctxt, void *render_ctxt, unsigned n_uniforms, const int *uniforms, const m4f_t *model_x, float alpha)
 {
-	play_t		*play = render_ctxt;
-	pig_t		*pig = uniforms_ctxt;
-	unsigned	t0, t1;
-	float		r = randf();
+	play_t			*play = render_ctxt;
+	pig_t			*pig = uniforms_ctxt;
+	unsigned		t0, t1;
+	float			r = randf();
+	const shader_uniform_t	*active_uniforms;
+	int			n_active_uniforms;
 
 	if (play_ticks_elapsed(play, PLAY_TICKS_TIMER2, 1000)) {
 		if (shader_reload_files(shader) < 0)
diff --git a/src/shader.c b/src/shader.c
index 1cadc7f..83df512 100644
--- a/src/shader.c
+++ b/src/shader.c
@@ -22,16 +22,20 @@
 #include "glad.h"
 #include "macros.h"
 
+#include "shader.h"
+
 
 typedef struct shader_t {
-	unsigned	program, refcnt;
-	unsigned	n_uniforms, n_attributes;
-	const char	**uniforms, **attributes;
-	int		*uniform_locations, *attribute_locations;
-	const char	*vs_path, *fs_path;
-	struct timespec	vs_mtime, fs_mtime;
-	
-	int		locations[];
+	unsigned		program, refcnt;
+	unsigned		n_uniforms, n_attributes;
+	const char		**uniforms, **attributes;
+	int			*uniform_locations, *attribute_locations;
+	const char		*vs_path, *fs_path;
+	struct timespec		vs_mtime, fs_mtime;
+	shader_uniform_t	*active_uniforms;
+	int			n_active_uniforms;
+
+	int			locations[];
 } shader_t;
 
 
@@ -81,6 +85,58 @@ unsigned int shader_pair_new_bare(const char *vs_src, const char *fs_src)
 	return shader;
 }
 
+
+/* query a shader for its active uniforms, returns results in res_uniforms
+ * the returned results are owned by the shader, do not free them, they will be
+ * cleaned up with shader_free() or reallocated by shader_reload_files()
+ */
+void shader_active_uniforms(shader_t *shader, int *res_n_uniforms, const shader_uniform_t **res_uniforms)
+{
+	assert(shader);
+	assert(res_n_uniforms);
+	assert(res_uniforms);
+
+	*res_n_uniforms = shader->n_active_uniforms;
+	*res_uniforms = shader->active_uniforms;
+}
+
+
+static void refresh_active_uniforms(shader_t *shader)
+{
+	int	n, maxlen;
+
+	assert(shader);
+
+	if (shader->active_uniforms) {
+		for (int i = 0; i < shader->n_active_uniforms; i++)
+			free(shader->active_uniforms[i].name);
+		free(shader->active_uniforms);
+		shader->active_uniforms = NULL;
+		shader->n_active_uniforms = 0;
+	}
+
+	glGetProgramiv(shader->program, GL_ACTIVE_UNIFORMS, &n);
+	glGetProgramiv(shader->program, GL_ACTIVE_UNIFORM_MAX_LENGTH, &maxlen);
+
+	/* FIXME: this is currently written such that allocation failures just cut the
+	 * active uniforms short instead of throwing an error, but should probably
+	 * be rewritten to fail and report the ENOMEM errors.
+	 */
+	shader->active_uniforms = calloc(n, sizeof(shader_uniform_t));
+	if (shader->active_uniforms) {
+		for (int i = 0; i < n; i++) {
+			shader->active_uniforms[i].name = calloc(maxlen, sizeof(char));
+			if (!shader->active_uniforms[i].name)
+				break;
+
+			glGetActiveUniform(shader->program, i, maxlen, /* length */ NULL, /* size */ NULL, &shader->active_uniforms[i].type, shader->active_uniforms[i].name);
+			shader->active_uniforms[i].location = glGetUniformLocation(shader->program, shader->active_uniforms[i].name);
+			shader->n_active_uniforms++;
+		}
+	}
+}
+
+
 static void get_locations(shader_t *shader)
 {
 	for (unsigned i = 0; i < shader->n_uniforms; i++)
@@ -90,6 +146,7 @@ static void get_locations(shader_t *shader)
 		shader->attribute_locations[i] = glGetAttribLocation(shader->program, shader->attributes[i]);
 }
 
+
 shader_t * shader_pair_new(const char *vs_src, const char *fs_src, unsigned n_uniforms, const char **uniforms, unsigned n_attributes, const char **attributes)
 {
 	shader_t	*shader;
@@ -112,6 +169,7 @@ shader_t * shader_pair_new(const char *vs_src, const char *fs_src, unsigned n_un
 	shader->attribute_locations = &shader->locations[n_uniforms];
 
 	get_locations(shader);
+	refresh_active_uniforms(shader);
 
 	return shader;
 }
@@ -178,6 +236,7 @@ int shader_reload_files(shader_t *shader)
 	free(fs_src);
 
 	get_locations(shader);
+	refresh_active_uniforms(shader);
 
 	return ret;
 }
diff --git a/src/shader.h b/src/shader.h
index b52189a..a7df2ec 100644
--- a/src/shader.h
+++ b/src/shader.h
@@ -19,6 +19,12 @@
 
 typedef struct shader_t shader_t;
 
+typedef struct shader_uniform_t {
+	char	*name;
+	GLenum	type;
+	int	location;
+} shader_uniform_t;
+
 unsigned int shader_pair_new_bare(const char *vs_src, const char *fs_src);
 shader_t * shader_pair_new(const char *vs_src, const char *fs_src, unsigned n_uniforms, const char **uniforms, unsigned n_attributes, const char **attributes);
 shader_t * shader_pair_new_files(const char *vs_path, const char *fs_path, unsigned n_uniforms, const char **uniforms, unsigned n_attributes, const char **attributes);
@@ -26,5 +32,6 @@ void shader_ref(shader_t *shader);
 shader_t * shader_free(shader_t *shader);
 void shader_use(shader_t *shader, unsigned *res_n_uniforms, int **res_uniform_locations, unsigned *res_n_attributes, int **res_attribute_locations);
 int shader_reload_files(shader_t *shader);
+void shader_active_uniforms(shader_t *shader, int *res_n_uniforms, const shader_uniform_t **res_uniforms);
 
 #endif