Added MSAA support for OpenGL ES contexts on iOS.

Note that extra steps must be taken when using glReadPixels to read the contents of the main OpenGL ES framebuffer on iOS, if multisampling is used. See the OpenGL ES section of README-ios.md for details.

src/video/uikit/SDL_uikitopengles.m

@@ -141,11 +141,16 @@ UIKit_GL_CreateContext(_THIS, SDL_Window * window)
         CGRect frame = UIKit_ComputeViewFrame(window, data.uiwindow.screen);
         EAGLSharegroup *sharegroup = nil;
         CGFloat scale = 1.0;
+        int samples = 0;
 
         /* The EAGLRenderingAPI enum values currently map 1:1 to major GLES
          * versions. */
         EAGLRenderingAPI api = _this->gl_config.major_version;
 
+        if (_this->gl_config.multisamplebuffers > 0) {
+            samples = _this->gl_config.multisamplesamples;
+        }
+
         if (_this->gl_config.share_with_current_context) {
             EAGLContext *context = (__bridge EAGLContext *) SDL_GL_GetCurrentContext();
             sharegroup = context.sharegroup;
@@ -182,6 +187,7 @@ UIKit_GL_CreateContext(_THIS, SDL_Window * window)
                                                 depthBits:_this->gl_config.depth_size
                                               stencilBits:_this->gl_config.stencil_size
                                                      sRGB:_this->gl_config.framebuffer_srgb_capable
+                                             multisamples:samples
                                                   context:context];
 
         if (!view) {

src/video/uikit/SDL_uikitopenglview.h

@@ -21,7 +21,7 @@
 
 #import <UIKit/UIKit.h>
 #import <OpenGLES/EAGL.h>
-#import <OpenGLES/ES2/gl.h>
+#import <OpenGLES/ES3/gl.h>
 
 #import "SDL_uikitview.h"
 #include "SDL_uikitvideo.h"
@@ -38,6 +38,7 @@
                     depthBits:(int)depthBits
                   stencilBits:(int)stencilBits
                          sRGB:(BOOL)sRGB
+                 multisamples:(int)multisamples
                       context:(EAGLContext *)glcontext;
 
 @property (nonatomic, readonly, weak) EAGLContext *context;
@@ -48,6 +49,7 @@
 
 @property (nonatomic, readonly) GLuint drawableRenderbuffer;
 @property (nonatomic, readonly) GLuint drawableFramebuffer;
+@property (nonatomic, readonly) GLuint msaaResolveFramebuffer;
 
 - (void)swapBuffers;
 

src/video/uikit/SDL_uikitopenglview.m

@@ -34,8 +34,18 @@
     /* The depth buffer that is attached to viewFramebuffer, if it exists. */
     GLuint depthRenderbuffer;
 
+    GLenum colorBufferFormat;
+
     /* format of depthRenderbuffer */
     GLenum depthBufferFormat;
+
+    /* The framebuffer and renderbuffer used for rendering with MSAA. */
+    GLuint msaaFramebuffer, msaaRenderbuffer;
+
+    /* The number of MSAA samples. */
+    int samples;
+
+    BOOL retainedBacking;
 }
 
 @synthesize context;
@@ -57,6 +67,7 @@
                     depthBits:(int)depthBits
                   stencilBits:(int)stencilBits
                          sRGB:(BOOL)sRGB
+                 multisamples:(int)multisamples
                       context:(EAGLContext *)glcontext
 {
     if ((self = [super initWithFrame:frame])) {
@@ -65,6 +76,8 @@
         NSString *colorFormat = nil;
 
         context = glcontext;
+        samples = multisamples;
+        retainedBacking = retained;
 
         if (!context || ![EAGLContext setCurrentContext:context]) {
             SDL_SetError("Could not create OpenGL ES drawable (could not make context current)");
@@ -75,6 +88,7 @@
             /* sRGB EAGL drawable support was added in iOS 7. */
             if (UIKit_IsSystemVersionAtLeast(7.0)) {
                 colorFormat = kEAGLColorFormatSRGBA8;
+                colorBufferFormat = GL_SRGB8_ALPHA8;
             } else {
                 SDL_SetError("sRGB drawables are not supported.");
                 return nil;
@@ -82,9 +96,11 @@
         } else if (rBits >= 8 || gBits >= 8 || bBits >= 8) {
             /* if user specifically requests rbg888 or some color format higher than 16bpp */
             colorFormat = kEAGLColorFormatRGBA8;
+            colorBufferFormat = GL_RGBA8;
         } else {
             /* default case (potentially faster) */
             colorFormat = kEAGLColorFormatRGB565;
+            colorBufferFormat = GL_RGB565;
         }
 
         CAEAGLLayer *eaglLayer = (CAEAGLLayer *)self.layer;
@@ -117,7 +133,31 @@
         glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_WIDTH, &backingWidth);
         glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_HEIGHT, &backingHeight);
 
-        if ((useDepthBuffer) || (useStencilBuffer)) {
+        if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE) {
+            SDL_SetError("Failed creating OpenGL ES framebuffer");
+            return nil;
+        }
+
+        /* When MSAA is used we'll use a separate framebuffer for rendering to,
+         * since we'll need to do an explicit MSAA resolve before presenting. */
+        if (samples > 0) {
+            glGenFramebuffers(1, &msaaFramebuffer);
+            glBindFramebuffer(GL_FRAMEBUFFER, msaaFramebuffer);
+
+            glGenRenderbuffers(1, &msaaRenderbuffer);
+            glBindRenderbuffer(GL_RENDERBUFFER, msaaRenderbuffer);
+
+            glRenderbufferStorageMultisample(GL_RENDERBUFFER, samples, colorBufferFormat, backingWidth, backingHeight);
+
+            glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, msaaRenderbuffer);
+
+            if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE) {
+                SDL_SetError("Failed creating OpenGL ES framebuffer: Unsupported MSAA sample count");
+                return nil;
+            }
+        }
+
+        if (useDepthBuffer || useStencilBuffer) {
             if (useStencilBuffer) {
                 /* Apparently you need to pack stencil and depth into one buffer. */
                 depthBufferFormat = GL_DEPTH24_STENCIL8_OES;
@@ -129,7 +169,13 @@
 
             glGenRenderbuffers(1, &depthRenderbuffer);
             glBindRenderbuffer(GL_RENDERBUFFER, depthRenderbuffer);
-            glRenderbufferStorage(GL_RENDERBUFFER, depthBufferFormat, backingWidth, backingHeight);
+
+            if (samples > 0) {
+                glRenderbufferStorageMultisample(GL_RENDERBUFFER, samples, depthBufferFormat, backingWidth, backingHeight);
+            } else {
+                glRenderbufferStorage(GL_RENDERBUFFER, depthBufferFormat, backingWidth, backingHeight);
+            }
+
             if (useDepthBuffer) {
                 glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, depthRenderbuffer);
             }
@@ -158,7 +204,23 @@
 
 - (GLuint)drawableFramebuffer
 {
-    return viewFramebuffer;
+    /* When MSAA is used, the MSAA draw framebuffer is used for drawing. */
+    if (msaaFramebuffer) {
+        return msaaFramebuffer;
+    } else {
+        return viewFramebuffer;
+    }
+}
+
+- (GLuint)msaaResolveFramebuffer
+{
+    /* When MSAA is used, the MSAA draw framebuffer is used for drawing and the
+     * view framebuffer is used as a MSAA resolve framebuffer. */
+    if (msaaFramebuffer) {
+        return viewFramebuffer;
+    } else {
+        return 0;
+    }
 }
 
 - (void)updateFrame
@@ -172,9 +234,19 @@
     glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_WIDTH, &backingWidth);
     glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_HEIGHT, &backingHeight);
 
+    if (msaaRenderbuffer != 0) {
+        glBindRenderbuffer(GL_RENDERBUFFER, msaaRenderbuffer);
+        glRenderbufferStorageMultisample(GL_RENDERBUFFER, samples, GL_RGBA8, backingWidth, backingHeight);
+    }
+
     if (depthRenderbuffer != 0) {
         glBindRenderbuffer(GL_RENDERBUFFER, depthRenderbuffer);
-        glRenderbufferStorage(GL_RENDERBUFFER, depthBufferFormat, backingWidth, backingHeight);
+
+        if (samples > 0) {
+            glRenderbufferStorageMultisample(GL_RENDERBUFFER, samples, depthBufferFormat, backingWidth, backingHeight);
+        } else {
+            glRenderbufferStorage(GL_RENDERBUFFER, depthBufferFormat, backingWidth, backingHeight);
+        }
     }
 
     glBindRenderbuffer(GL_RENDERBUFFER, prevRenderbuffer);
@@ -197,10 +269,47 @@
             glLabelObjectEXT(GL_RENDERBUFFER, depthRenderbuffer, 0, "context depth buffer");
         }
     }
+
+    if (msaaFramebuffer != 0) {
+        glLabelObjectEXT(GL_FRAMEBUFFER, msaaFramebuffer, 0, "context MSAA FBO");
+    }
+
+    if (msaaRenderbuffer != 0) {
+        glLabelObjectEXT(GL_RENDERBUFFER, msaaRenderbuffer, 0, "context MSAA renderbuffer");
+    }
 }
 
 - (void)swapBuffers
 {
+    if (msaaFramebuffer) {
+        const GLenum attachments[] = {GL_COLOR_ATTACHMENT0};
+
+        glBindFramebuffer(GL_DRAW_FRAMEBUFFER, viewFramebuffer);
+
+        /* OpenGL ES 3+ provides explicit MSAA resolves via glBlitFramebuffer.
+         * In OpenGL ES 1 and 2, MSAA resolves must be done via an extension. */
+        if (context.API >= kEAGLRenderingAPIOpenGLES3) {
+            int w = backingWidth;
+            int h = backingHeight;
+            glBlitFramebuffer(0, 0, w, h, 0, 0, w, h, GL_COLOR_BUFFER_BIT, GL_NEAREST);
+
+            if (!retainedBacking) {
+                /* Discard the contents of the MSAA drawable color buffer. */
+                glInvalidateFramebuffer(GL_READ_FRAMEBUFFER, 1, attachments);
+            }
+        } else {
+            glResolveMultisampleFramebufferAPPLE();
+
+            if (!retainedBacking) {
+                glDiscardFramebufferEXT(GL_READ_FRAMEBUFFER, 1, attachments);
+            }
+        }
+
+        /* We assume the "drawable framebuffer" (MSAA draw framebuffer) was
+         * previously bound... */
+        glBindFramebuffer(GL_DRAW_FRAMEBUFFER, msaaFramebuffer);
+    }
+
     /* viewRenderbuffer should always be bound here. Code that binds something
      * else is responsible for rebinding viewRenderbuffer, to reduce duplicate
      * state changes. */
@@ -245,6 +354,16 @@
         glDeleteRenderbuffers(1, &depthRenderbuffer);
         depthRenderbuffer = 0;
     }
+
+    if (msaaFramebuffer != 0) {
+        glDeleteFramebuffers(1, &msaaFramebuffer);
+        msaaFramebuffer = 0;
+    }
+
+    if (msaaRenderbuffer != 0) {
+        glDeleteRenderbuffers(1, &msaaRenderbuffer);
+        msaaRenderbuffer = 0;
+    }
 }
 
 - (void)dealloc

src/video/uikit/SDL_uikitwindow.m

@@ -339,9 +339,11 @@ UIKit_GetWindowWMInfo(_THIS, SDL_Window * window, SDL_SysWMinfo * info)
                     SDL_uikitopenglview *glview = (SDL_uikitopenglview *)data.viewcontroller.view;
                     info->info.uikit.framebuffer = glview.drawableFramebuffer;
                     info->info.uikit.colorbuffer = glview.drawableRenderbuffer;
+                    info->info.uikit.resolveFramebuffer = glview.msaaResolveFramebuffer;
                 } else {
                     info->info.uikit.framebuffer = 0;
                     info->info.uikit.colorbuffer = 0;
+                    info->info.uikit.resolveFramebuffer = 0;
                 }
             }