Use simpler, faster shader when brightness, contrast, hue and saturation are unchanged

src/ol/renderer/webgl/webglmapdefault.glsl

@@ -0,0 +1,30 @@
+//! NAMESPACE=ol.renderer.webgl.map.shader.Default
+//! CLASS=ol.renderer.webgl.map.shader.Default
+
+
+//! COMMON
+varying vec2 v_texCoord;
+
+
+//! VERTEX
+attribute vec2 a_position;
+attribute vec2 a_texCoord;
+
+uniform mat4 u_texCoordMatrix;
+uniform mat4 u_projectionMatrix;
+
+void main(void) {
+  gl_Position = u_projectionMatrix * vec4(a_position, 0., 1.);
+  v_texCoord = (u_texCoordMatrix * vec4(a_texCoord, 0., 1.)).st;
+}
+
+
+//! FRAGMENT
+uniform float u_opacity;
+uniform sampler2D u_texture;
+
+void main(void) {
+  vec4 texColor = texture2D(u_texture, v_texCoord);
+  gl_FragColor.rgb = texColor.rgb;
+  gl_FragColor.a = texColor.a * u_opacity;
+}