[ios] Custom style layer

Exposed Map::addCustomLayer() publicly as an undocumented, block-based API. This change avoids the terms “layer”, “initialize”, “render”, and “altitude” because they overload existing terminology in the SDK, UIKit, or MapKit. (“Layer” is qualified as “style layer”.) There are outstanding questions about ARC memory management, but this approach works in both Objective-C and Swift for pure OpenGL programming.

Added a demo to iosapp that draws a green layer below any labels in Mapbox Streets.

1 files changed, 59 insertions, 0 deletions

diff --git a/ios/app/MBXViewController.mm b/ios/app/MBXViewController.mm
index 7e19382f9a..d5ef815351 100644
--- a/ios/app/MBXViewController.mm
+++ b/ios/app/MBXViewController.mm
@@ -4,6 +4,7 @@
 #import <mbgl/util/default_styles.hpp>
 
 #import <CoreLocation/CoreLocation.h>
+#import <OpenGLES/ES2/gl.h>
 
 static UIColor *const kTintColor = [UIColor colorWithRed:0.120 green:0.550 blue:0.670 alpha:1.000];
 
@@ -150,6 +151,7 @@ static const CLLocationCoordinate2D WorldTourDestinations[] = {
                                                                 @"Add Test Shapes",
                                                                 @"Start World Tour",
                                                                 @"Remove Annotations",
+                                                                @"Insert Custom Style Layer",
                                                                 nil];
 
     [sheet showFromBarButtonItem:self.navigationItem.leftBarButtonItem animated:YES];
@@ -260,6 +262,10 @@ static const CLLocationCoordinate2D WorldTourDestinations[] = {
     {
         [self.mapView removeAnnotations:self.mapView.annotations];
     }
+    else if (buttonIndex == actionSheet.firstOtherButtonIndex + 9)
+    {
+        [self insertCustomStyleLayer];
+    }
 }
 
 - (void)parseFeaturesAddingCount:(NSUInteger)featuresCount
@@ -302,6 +308,59 @@ static const CLLocationCoordinate2D WorldTourDestinations[] = {
     });
 }
 
+- (void)insertCustomStyleLayer
+{
+    static const GLchar *vertexShaderSource = "attribute vec2 a_pos; void main() { gl_Position = vec4(a_pos, 0, 1); }";
+    static const GLchar *fragmentShaderSource = "void main() { gl_FragColor = vec4(0, 1, 0, 1); }";
+    
+    __block GLuint program = 0;
+    __block GLuint vertexShader = 0;
+    __block GLuint fragmentShader = 0;
+    __block GLuint buffer = 0;
+    __block GLuint a_pos = 0;
+    [self.mapView insertCustomStyleLayerWithIdentifier:@"mbx-custom" preparationHandler:^{
+        program = glCreateProgram();
+        vertexShader = glCreateShader(GL_VERTEX_SHADER);
+        fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
+        
+        glShaderSource(vertexShader, 1, &vertexShaderSource, nullptr);
+        glCompileShader(vertexShader);
+        glAttachShader(program, vertexShader);
+        glShaderSource(fragmentShader, 1, &fragmentShaderSource, nullptr);
+        glCompileShader(fragmentShader);
+        glAttachShader(program, fragmentShader);
+        glLinkProgram(program);
+        a_pos = glGetAttribLocation(program, "a_pos");
+        
+        GLfloat background[] = { -1,-1, 1,-1, -1,1, 1,1 };
+        glGenBuffers(1, &buffer);
+        glBindBuffer(GL_ARRAY_BUFFER, buffer);
+        glBufferData(GL_ARRAY_BUFFER, 8 * sizeof(GLfloat), background, GL_STATIC_DRAW);
+    } drawingHandler:^(__unused CGSize size,
+                       __unused CLLocationCoordinate2D centerCoordinate,
+                       __unused double zoomLevel,
+                       __unused CLLocationDirection direction,
+                       __unused CGFloat pitch,
+                       __unused CGFloat perspectiveSkew) {
+        glUseProgram(program);
+        glBindBuffer(GL_ARRAY_BUFFER, buffer);
+        glEnableVertexAttribArray(a_pos);
+        glVertexAttribPointer(a_pos, 2, GL_FLOAT, GL_FALSE, 0, NULL);
+        glDisable(GL_STENCIL_TEST);
+        glDisable(GL_DEPTH_TEST);
+        glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
+    } completionHandler:^{
+        if (program) {
+            glDeleteBuffers(1, &buffer);
+            glDetachShader(program, vertexShader);
+            glDetachShader(program, fragmentShader);
+            glDeleteShader(vertexShader);
+            glDeleteShader(fragmentShader);
+            glDeleteProgram(program);
+        }
+    } belowStyleLayerWithIdentifier:@"housenum-label"];
+}
+
 - (void)handleLongPress:(UILongPressGestureRecognizer *)longPress
 {
     if (longPress.state == UIGestureRecognizerStateBegan)