Auto merge of #16626 - BorisChiou:animation/timing_function/frames, r=emilio

Implement frames timing function

A frames timing function is a type of timing function that divides the input time into a specified number of intervals of equal length, each of which is associated with an output progress value of increasing value.

---
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #15740.
- [X] There are tests for these changes, and web-platform-tests/css-timing-1 also provides tests.

components/style/animation.rs

@@ -352,6 +352,22 @@ impl PropertyAnimation {
             TransitionTimingFunction::Steps(steps, StartEnd::End) => {
                 (time * (steps as f64)).floor() / (steps as f64)
             }
+            TransitionTimingFunction::Frames(frames) => {
+                // https://drafts.csswg.org/css-timing/#frames-timing-functions
+                let mut out = (time * (frames as f64)).floor() / ((frames - 1) as f64);
+                if out > 1.0 {
+                    // FIXME: Basically, during the animation sampling process, the input progress
+                    // should be in the range of [0, 1]. However, |time| is not accurate enough
+                    // here, which means |time| could be larger than 1.0 in the last animation
+                    // frame. (It should be equal to 1.0 exactly.) This makes the output of frames
+                    // timing function jumps to the next frame/level.
+                    // However, this solution is still not correct because |time| is possible
+                    // outside the range of [0, 1] after introducing Web Animations. We should fix
+                    // this problem when implementing web animations.
+                    out = 1.0;
+                }
+                out
+            }
         };
 
         self.property.update(style, progress);

components/style/gecko_bindings/sugar/ns_timing_function.rs

@@ -21,6 +21,13 @@ impl nsTimingFunction {
         }
     }
 
+    fn set_as_frames(&mut self, frames: u32) {
+        self.mType = nsTimingFunction_Type::Frames;
+        unsafe {
+            self.__bindgen_anon_1.__bindgen_anon_1.as_mut().mStepsOrFrames = frames;
+        }
+    }
+
     fn set_as_bezier(&mut self,
                      function_type: nsTimingFunction_Type,
                      p1: Point2D<f32>,
@@ -48,6 +55,9 @@ impl From<ComputedTimingFunction> for nsTimingFunction {
             ComputedTimingFunction::Steps(steps, StartEnd::End) => {
                 tf.set_as_step(nsTimingFunction_Type::StepEnd, steps);
             },
+            ComputedTimingFunction::Frames(frames) => {
+                tf.set_as_frames(frames);
+            },
             ComputedTimingFunction::CubicBezier(p1, p2) => {
                 tf.set_as_bezier(nsTimingFunction_Type::CubicBezier, p1, p2);
             },
@@ -69,6 +79,10 @@ impl From<SpecifiedTimingFunction> for nsTimingFunction {
                 debug_assert!(steps.value() >= 0);
                 tf.set_as_step(nsTimingFunction_Type::StepEnd, steps.value() as u32);
             },
+            SpecifiedTimingFunction::Frames(frames) => {
+                debug_assert!(frames.value() >= 2);
+                tf.set_as_frames(frames.value() as u32);
+            },
             SpecifiedTimingFunction::CubicBezier(p1, p2) => {
                 tf.set_as_bezier(nsTimingFunction_Type::CubicBezier,
                                  Point2D::new(p1.x.get(), p1.y.get()),
@@ -104,6 +118,9 @@ impl From<SpecifiedTimingFunction> for nsTimingFunction {
                         debug_assert!(keyword == FunctionKeyword::StepEnd && steps == 1);
                         tf.set_as_step(nsTimingFunction_Type::StepEnd, steps);
                     },
+                    ComputedTimingFunction::Frames(frames) => {
+                        tf.set_as_frames(frames)
+                    }
                 }
             },
         }
@@ -125,8 +142,8 @@ impl From<nsTimingFunction> for ComputedTimingFunction {
                     StartEnd::End)
             },
             nsTimingFunction_Type::Frames => {
-                // https://github.com/servo/servo/issues/15740
+                ComputedTimingFunction::Frames(
-                panic!("Frames timing function is not support yet");
+                    unsafe { function.__bindgen_anon_1.__bindgen_anon_1.as_ref().mStepsOrFrames })
             }
             nsTimingFunction_Type::Ease |
             nsTimingFunction_Type::Linear |

components/style/properties/longhand/box.mako.rs

@@ -511,6 +511,7 @@ ${helpers.single_keyword("overflow-x", "visible hidden scroll auto",
         pub enum T {
             CubicBezier(Point2D<f32>, Point2D<f32>),
             Steps(u32, StartEnd),
+            Frames(u32),
         }
 
         impl ToCss for T {
@@ -528,10 +529,15 @@ ${helpers.single_keyword("overflow-x", "visible hidden scroll auto",
                         try!(dest.write_str(", "));
                         try!(p2.y.to_css(dest));
                         dest.write_str(")")
-                    }
+                    },
                     T::Steps(steps, start_end) => {
                         super::serialize_steps(dest, specified::Integer::new(steps as i32), start_end)
-                    }
+                    },
+                    T::Frames(frames) => {
+                        try!(dest.write_str("frames("));
+                        try!(frames.to_css(dest));
+                        dest.write_str(")")
+                    },
                 }
             }
         }
@@ -569,6 +575,7 @@ ${helpers.single_keyword("overflow-x", "visible hidden scroll auto",
     pub enum SpecifiedValue {
         CubicBezier(Point2D<Number>, Point2D<Number>),
         Steps(specified::Integer, StartEnd),
+        Frames(specified::Integer),
         Keyword(FunctionKeyword),
     }
 
@@ -617,6 +624,13 @@ ${helpers.single_keyword("overflow-x", "visible hidden scroll auto",
                         }));
                         Ok(SpecifiedValue::Steps(step_count, start_end))
                     },
+                    "frames" => {
+                        // https://drafts.csswg.org/css-timing/#frames-timing-functions
+                        let frames = try!(input.parse_nested_block(|input| {
+                            specified::Integer::parse_with_minimum(context, input, 2)
+                        }));
+                        Ok(SpecifiedValue::Frames(frames))
+                    },
                     _ => Err(())
                 }
             }
@@ -655,6 +669,11 @@ ${helpers.single_keyword("overflow-x", "visible hidden scroll auto",
                 SpecifiedValue::Steps(steps, start_end) => {
                     serialize_steps(dest, steps, start_end)
                 },
+                SpecifiedValue::Frames(frames) => {
+                    try!(dest.write_str("frames("));
+                    try!(frames.to_css(dest));
+                    dest.write_str(")")
+                },
                 SpecifiedValue::Keyword(keyword) => {
                     match keyword {
                         FunctionKeyword::StepStart => {
@@ -686,6 +705,9 @@ ${helpers.single_keyword("overflow-x", "visible hidden scroll auto",
                 SpecifiedValue::Steps(count, start_end) => {
                     computed_value::T::Steps(count.to_computed_value(context) as u32, start_end)
                 },
+                SpecifiedValue::Frames(frames) => {
+                    computed_value::T::Frames(frames.to_computed_value(context) as u32)
+                },
                 SpecifiedValue::Keyword(keyword) => keyword.to_computed_value(),
             }
         }
@@ -703,6 +725,10 @@ ${helpers.single_keyword("overflow-x", "visible hidden scroll auto",
                     let int_count = count as i32;
                     SpecifiedValue::Steps(specified::Integer::from_computed_value(&int_count), start_end)
                 },
+                computed_value::T::Frames(frames) => {
+                    let frames = frames as i32;
+                    SpecifiedValue::Frames(specified::Integer::from_computed_value(&frames))
+                },
             }
         }
     }

components/style/values/specified/mod.rs

@@ -845,7 +845,8 @@ impl Parse for Integer {
 }
 
 impl Integer {
-    fn parse_with_minimum(context: &ParserContext, input: &mut Parser, min: i32) -> Result<Integer, ()> {
+    #[allow(missing_docs)]
+    pub fn parse_with_minimum(context: &ParserContext, input: &mut Parser, min: i32) -> Result<Integer, ()> {
         match parse_integer(context, input) {
             Ok(value) if value.value() >= min => Ok(value),
             _ => Err(()),

tests/unit/style/parsing/transition_timing_function.rs

@@ -25,9 +25,29 @@ fn test_cubic_bezier() {
 #[test]
 fn test_steps() {
     assert_roundtrip_with_context!(transition_timing_function::parse, "steps(1)");
+    assert_roundtrip_with_context!(transition_timing_function::parse, "steps(  1)", "steps(1)");
+    assert_roundtrip_with_context!(transition_timing_function::parse, "steps(1, start)");
+    assert_roundtrip_with_context!(transition_timing_function::parse, "steps(2, end) ", "steps(2)");
 
     // Step interval value must be an integer greater than 0
     assert!(parse(transition_timing_function::parse, "steps(0)").is_err());
     assert!(parse(transition_timing_function::parse, "steps(0.5)").is_err());
     assert!(parse(transition_timing_function::parse, "steps(-1)").is_err());
+    assert!(parse(transition_timing_function::parse, "steps(1, middle)").is_err());
+}
+
+#[test]
+fn test_frames() {
+    assert_roundtrip_with_context!(transition_timing_function::parse, "frames(  2 )", "frames(2)");
+    assert_roundtrip_with_context!(transition_timing_function::parse, "frames(10000)");
+
+    // Frames number must be an integer greater than 1
+    assert!(parse(transition_timing_function::parse, "frames(1)").is_err());
+    assert!(parse(transition_timing_function::parse, "frames(-2)").is_err());
+    assert!(parse(transition_timing_function::parse, "frames()").is_err());
+    assert!(parse(transition_timing_function::parse, "frames(,)").is_err());
+    assert!(parse(transition_timing_function::parse, "frames(a)").is_err());
+    assert!(parse(transition_timing_function::parse, "frames(2.0)").is_err());
+    assert!(parse(transition_timing_function::parse, "frames(2.5)").is_err());
+    assert!(parse(transition_timing_function::parse, "frames(2 3)").is_err());
 }

tests/unit/style/properties/serialization.rs

@@ -1209,6 +1209,32 @@ mod shorthand_serialization {
 
             assert_eq!(serialization, block_text);
         }
+
+        #[test]
+        fn transition_should_serialize_acceptable_step_timing_function() {
+            let block_text = "transition-property: margin-left; \
+                              transition-duration: 3s; \
+                              transition-delay: 4s; \
+                              transition-timing-function: steps(2, start);";
+            let block = parse(|c, i| Ok(parse_property_declaration_list(c, i)), block_text).unwrap();
+
+            let serialization = block.to_css_string();
+
+            assert_eq!(serialization, "transition: margin-left 3s steps(2, start) 4s;");
+        }
+
+        #[test]
+        fn transition_should_serialize_acceptable_frames_timing_function() {
+            let block_text = "transition-property: margin-left; \
+                              transition-duration: 3s; \
+                              transition-delay: 4s; \
+                              transition-timing-function: frames(2);";
+            let block = parse(|c, i| Ok(parse_property_declaration_list(c, i)), block_text).unwrap();
+
+            let serialization = block.to_css_string();
+
+            assert_eq!(serialization, "transition: margin-left 3s frames(2) 4s;");
+        }
     }
 
     mod keywords {