use LINEAR magFilter when dpr !== 1

Author: fuzhenn

packages/maptalks/src/renderer/layer/ImageGLRenderable.ts

@@ -418,7 +418,6 @@ const ImageGLRenderable = function <T extends MixinConstructor>(Base: T) {
          * @param image
          */
         loadTexture(image: TileImageType, resized = false): TileImageTexture {
-            const map = (this as any).getMap();
             const gl = this.gl;
             let texture = image.texture;   // Create a texture object
             if (!texture) {
@@ -428,12 +427,14 @@ const ImageGLRenderable = function <T extends MixinConstructor>(Base: T) {
             gl.bindTexture(gl.TEXTURE_2D, texture);
             const genMipmap = this.layer.options['mipmapTexture'];
             if (genMipmap) {
+                const map = (this as any).getMap();
+                const dpr = map.getDevicePixelRatio();
                 if (map.isMoving() && map.getRenderer().isViewChanged()) {
                     gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR_MIPMAP_LINEAR);
                 } else {
                     gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR);
                 }
-                if (resized) {
+                if (dpr !== 1 || resized) {
                     gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR);
                 } else {
                     gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.NEAREST);