完善 shader，修复部分视频（非 16 倍数宽高）绘制不准确问题，同时避免黑边黑影问题

android/alpha_player/src/main/assets/frag.sh

@@ -1,15 +1,11 @@
 #extension GL_OES_EGL_image_external : require
 precision mediump float;
-varying vec2 vTextureCoord;
 uniform samplerExternalOES sTexture;
+varying highp vec2 l_TexCoordinate;
+varying highp vec2 r_TexCoordinate;
 
 void main() {
-    vec4 color = texture2D(sTexture, vTextureCoord);
-    vec4 color2Map = vec4(1.0, 1.0, 1.0, 1.0);
-    if (vTextureCoord.x >= 0.5) {
-        color2Map = texture2D(sTexture, vec2(vTextureCoord.x - 0.5, vTextureCoord.y));
-        gl_FragColor = vec4(color.r, color.g, color.b, color2Map.g);
-    } else {
-        gl_FragColor = vec4(color.r, color.g, color.b, color.a);
-    }
+    vec4 color = texture2D(sTexture, r_TexCoordinate);
+    vec4 alpha = texture2D(sTexture, vec2(l_TexCoordinate.x, l_TexCoordinate.y));
+    gl_FragColor = vec4(color.rgb, alpha.r);
 }

android/alpha_player/src/main/assets/vertex.sh

@@ -4,9 +4,12 @@ uniform mat4 uSTMatrix;
 attribute vec4 aPosition;
 attribute vec4 aTextureCoord;
 
-varying vec2 vTextureCoord;
+varying highp vec2 l_TexCoordinate;
+varying highp vec2 r_TexCoordinate;
 
 void main() {
     gl_Position = uMVPMatrix * aPosition;
-    vTextureCoord = (uSTMatrix * aTextureCoord).xy;
+    r_TexCoordinate = (uSTMatrix * aTextureCoord).xy;
+    float midX = (uSTMatrix * vec4(0.5, 0.0, 0.0, 1.0)).x;
+    l_TexCoordinate = vec2(r_TexCoordinate.x - midX, r_TexCoordinate.y);
 }