QoL: Optionally use overloaded env vars per target (#53)

README.md

@@ -44,6 +44,12 @@ files and libraries:
 * `FFMPEG_INCLUDE_DIR` - path to the FFmpeg header files
 * `FFMPEG_LIB_DIR` - path to the FFmpeg libs
 
+If you require building for multiple platforms, you can append `_PLATFORM_TARGET_TRIPLET` to both of the above to create platform specific env. variables, for example:
+* `FFMPEG_INCLUDE_DIR_AARCH64_LINUX_ANDROID = ${jniInclude}/arm64-v8a/`
+* `FFMPEG_LIB_DIR_AARCH64_LINUX_ANDROID     = ${jniLibs}/arm64-v8a/`
+* `FFMPEG_INCLUDE_DIR_X86_64_LINUX_ANDROID = ${jniInclude}/x86_64/`
+* `FFMPEG_LIB_DIR_X86_64_LINUX_ANDROID     = ${jniLibs}/x86_64/`
+
 If you prefer static linking, you can force it using:
 
 * `FFMPEG_STATIC=1`

build.rs

@@ -58,7 +58,15 @@ fn main() {
 }
 
 fn ffmpeg_include_dirs() -> Vec<PathBuf> {
-    if let Ok(dir) = env::var("FFMPEG_INCLUDE_DIR") {
+    if let Some(target) = normalized_target() {
+        if let Ok(dir) = env::var(&format!("FFMPEG_INCLUDE_DIR_{}", target)) {
+            let dir = PathBuf::from(dir);
+
+            if dir.is_dir() {
+                return vec![dir];
+            }
+        }
+    } else if let Ok(dir) = env::var("FFMPEG_INCLUDE_DIR") {
         let dir = PathBuf::from(dir);
 
         if dir.is_dir() {
@@ -78,7 +86,15 @@ fn ffmpeg_include_dirs() -> Vec<PathBuf> {
 }
 
 fn ffmpeg_lib_dirs() -> Vec<PathBuf> {
-    if let Ok(dir) = env::var("FFMPEG_LIB_DIR") {
+    if let Some(target) = normalized_target() {
+        if let Ok(dir) = env::var(&format!("FFMPEG_LIB_DIR_{}", target)) {
+            let dir = PathBuf::from(dir);
+
+            if dir.is_dir() {
+                return vec![dir];
+            }
+        }
+    } else if let Ok(dir) = env::var("FFMPEG_LIB_DIR") {
         let dir = PathBuf::from(dir);
 
         if dir.is_dir() {
@@ -97,6 +113,12 @@ fn ffmpeg_lib_dirs() -> Vec<PathBuf> {
     lib.link_paths
 }
 
+fn normalized_target() -> Option<String> {
+    env::var("TARGET")
+        .ok()
+        .map(|t| t.to_uppercase().replace('-', "_"))
+}
+
 fn link_static(lib: &str) {
     link(lib, "static")
 }