GL: Remove redundant use() call.

This is already called in GlUtil.Program().

Tested by confirming that the demo-gl target still runs as expected.

Refactoring change only. No intended functional changes.

PiperOrigin-RevId: 412308564

library/common/src/main/java/com/google/android/exoplayer2/util/GlUtil.java

@@ -42,7 +42,7 @@
 import java.util.Map;
 import javax.microedition.khronos.egl.EGL10;
 
-/** GL utilities. */
+/** OpenGL ES 2.0 utilities. */
 public final class GlUtil {
 
   /** Thrown when an OpenGL error occurs and {@link #glAssertionsEnabled} is {@code true}. */
@@ -85,7 +85,10 @@ public Program(Context context, String vertexShaderFilePath, String fragmentShad
     }
 
     /**
-     * Compiles a GL shader program from vertex and fragment shader GLSL GLES20 code.
+     * Creates a GL shader program from vertex and fragment shader GLSL GLES20 code.
+     *
+     * <p>This involves slow steps, like compiling, linking, and switching the GL program, so do not
+     * call this in fast rendering loops.
      *
      * @param vertexShaderGlsl The vertex shader program.
      * @param fragmentShaderGlsl The fragment shader program.
@@ -128,8 +131,14 @@ public Program(String vertexShaderGlsl, String fragmentShaderGlsl) {
       checkGlError();
     }
 
-    /** Uses the program. */
+    /**
+     * Uses the program.
+     *
+     * <p>Call this in the rendering loop to switch between different programs.
+     */
     public void use() {
+      // TODO(http://b/205002913): When multiple GL programs are supported by Transformer, make sure
+      // to call use() to switch between programs.
       GLES20.glUseProgram(programId);
       checkGlError();
     }

library/core/src/main/java/com/google/android/exoplayer2/video/VideoDecoderGLSurfaceView.java

@@ -166,7 +166,6 @@ public Renderer(GLSurfaceView surfaceView) {
     @Override
     public void onSurfaceCreated(GL10 unused, EGLConfig config) {
       program = new GlUtil.Program(VERTEX_SHADER, FRAGMENT_SHADER);
-      program.use();
       int posLocation = program.getAttributeArrayLocationAndEnable("in_pos");
       GLES20.glVertexAttribPointer(
           posLocation,

library/core/src/main/java/com/google/android/exoplayer2/video/spherical/ProjectionRenderer.java

@@ -15,7 +15,6 @@
  */
 package com.google.android.exoplayer2.video.spherical;
 
-import static com.google.android.exoplayer2.util.Assertions.checkNotNull;
 import static com.google.android.exoplayer2.util.GlUtil.checkGlError;
 
 import android.opengl.GLES11Ext;
@@ -139,9 +138,6 @@ public void draw(int textureId, float[] mvpMatrix, boolean rightEye) {
     }
 
     // Configure shader.
-    checkNotNull(program).use();
-    checkGlError();
-
     float[] texMatrix;
     if (stereoMode == C.STEREO_MODE_TOP_BOTTOM) {
       texMatrix = rightEye ? TEX_MATRIX_BOTTOM : TEX_MATRIX_TOP;