Add comments describing shader programs

PiperOrigin-RevId: 425885803

library/transformer/src/main/assets/shaders/fragment_shader_copy_external.glsl

@@ -11,6 +11,10 @@
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
+
+// Fragment shader that samples from an external texture with uTexSampler,
+// copying from this texture to the current output.
+
 #extension GL_OES_EGL_image_external : require
 precision mediump float;
 uniform samplerExternalOES uTexSampler;

library/transformer/src/main/assets/shaders/fragment_shader_copy_external_yuv_es3.glsl

@@ -12,6 +12,13 @@
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
+
+// ES 3 fragment shader that samples from an external texture with uTexSampler,
+// copying from this texture to the current output while applying the specified
+// color transform uColorTransform, which should be a YUV to RGB conversion
+// matrix. The sampler uses the using the EXT_YUV_target extension:
+// https://www.khronos.org/registry/OpenGL/extensions/EXT/EXT_YUV_target.txt.
+
 #extension GL_OES_EGL_image_external : require
 #extension GL_EXT_YUV_target : require
 precision mediump float;

library/transformer/src/main/assets/shaders/vertex_shader_transformation.glsl

@@ -11,6 +11,10 @@
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
+
+// Vertex shader that applies the 4 * 4 transformation matrix
+// uTransformationMatrix.
+
 attribute vec4 aFramePosition;
 attribute vec4 aTexCoords;
 uniform mat4 uTexTransform;

library/transformer/src/main/assets/shaders/vertex_shader_transformation_es3.glsl

@@ -12,6 +12,10 @@
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
+
+// ES 3 vertex shader that applies the 4 * 4 transformation matrix
+// uTransformationMatrix.
+
 in vec4 aFramePosition;
 in vec4 aTexCoords;
 uniform mat4 uTexTransform;