Add an example for using effects with the engine.

examples/engine_effects.c

+/*
+Demonstrates how to apply an effect to sounds using the high level engine API.
+
+This example will load a file from the command line and apply an echo/delay effect to it. It will
+show you how to manage `ma_sound` objects and how to insert an effect into the graph.
+
+The `ma_engine` object is a node graph and is compatible with the `ma_node_graph` API. The
+`ma_sound` object is a node within the node and is compatible with the `ma_node` API. This means
+that applying an effect is as simple as inserting an effect node into the node graph and plugging
+in the sound's output into the effect's input. See the "node_graph" example for how to use the
+node graph API.
+
+This example is playing only a single sound at a time which means only a single `ma_sound` object
+it being used. If you want to play multiple sounds at the same time, even if they're for the same
+sound file, you need multiple `ma_sound` objects.
+*/
+#define MINIAUDIO_IMPLEMENTATION
+#include "../miniaudio.h"
+
+#define DELAY_IN_SECONDS    0.2f
+#define DECAY               0.25f   /* Volume falloff for each echo. */
+
+static ma_engine g_engine;
+static ma_sound g_sound;            /* This example will play only a single sound at once, so we only need one `ma_sound` object. */
+static ma_delay_node g_delayNode;   /* The echo effect is achieved using a delay node. */
+
+int main(int argc, char** argv)
+{
+    ma_result result;
+
+    if (argc < 2) {
+        printf("No input file.");
+        return -1;
+    }
+
+    /* The engine needs to be initialized first. */
+    result = ma_engine_init(NULL, &g_engine);
+    if (result != MA_SUCCESS) {
+        printf("Failed to initialize audio engine.");
+        return -1;
+    }
+
+
+    /*
+    We'll build our graph starting from the end so initialize the delay node now. The output of
+    this node will be connected straight to the output. You could also attach it to a sound group
+    or any other node that accepts an input.
+
+    Creating a node requires a pointer to the node graph that owns it. The engine itself is a node
+    graph. In the code below we can get a pointer to the node graph with `ma_engine_get_node_graph()`
+    or we could simple cast the engine to a ma_node_graph* like so:
+    
+        (ma_node_graph*)&g_engine
+
+    The endpoint of the graph can be retrieved with `ma_engine_get_endpoint()`.
+    */
+    {
+        ma_delay_node_config delayNodeConfig;
+        ma_uint32 channels;
+        ma_uint32 sampleRate;
+
+        channels   = ma_engine_get_channels(&g_engine);
+        sampleRate = ma_engine_get_sample_rate(&g_engine);
+
+        delayNodeConfig = ma_delay_node_config_init(channels, sampleRate, (ma_uint32)(sampleRate * DELAY_IN_SECONDS), DECAY);
+
+        result = ma_delay_node_init(ma_engine_get_node_graph(&g_engine), &delayNodeConfig, NULL, &g_delayNode);
+        if (result != MA_SUCCESS) {
+            printf("Failed to initialize delay node.");
+            return -1;
+        }
+
+        /* Connect the output bus of the delay node to the input bus of the endpoint. */
+        ma_node_attach_output_bus(&g_delayNode, 0, ma_engine_get_endpoint(&g_engine), 0);
+    }
+
+
+    /* Now we can load the sound and connect it to the delay node. */
+    {
+        result = ma_sound_init_from_file(&g_engine, argv[1], 0, NULL, NULL, &g_sound);
+        if (result != MA_SUCCESS) {
+            printf("Failed to initialize sound \"%s\".", argv[1]);
+            return -1;
+        }
+
+        /* Connect the output of the sound to the input of the effect. */
+        ma_node_attach_output_bus(&g_sound, 0, &g_delayNode, 0);
+
+        /*
+        Start the sound after it's applied to the sound. Otherwise there could be a scenario where
+        the very first part of it is read before the attachment to the effect is made.
+        */
+        ma_sound_start(&g_sound);
+    }
+
+
+    printf("Press Enter to quit...");
+    getchar();
+
+    ma_sound_uninit(&g_sound);
+    ma_delay_node_uninit(&g_delayNode, NULL);
+    ma_engine_uninit(&g_engine);
+
+    return 0;
+}
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