1 #ifndef DALI_TOOLKIT_SHADER_EFFECT_MOTION_STRETCH_H
2 #define DALI_TOOLKIT_SHADER_EFFECT_MOTION_STRETCH_H
5 * Copyright (c) 2020 Samsung Electronics Co., Ltd.
7 * Licensed under the Apache License, Version 2.0 (the "License");
8 * you may not use this file except in compliance with the License.
9 * You may obtain a copy of the License at
11 * http://www.apache.org/licenses/LICENSE-2.0
13 * Unless required by applicable law or agreed to in writing, software
14 * distributed under the License is distributed on an "AS IS" BASIS,
15 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
16 * See the License for the specific language governing permissions and
17 * limitations under the License.
22 #include <dali/public-api/actors/actor.h>
23 #include <dali/public-api/animation/constraint.h>
24 #include <dali/public-api/object/property-map.h>
25 #include <dali/public-api/rendering/shader.h>
28 #include <dali-toolkit/public-api/visuals/visual-properties.h>
35 * @brief Set the properties for the motion stretch
37 inline void SetMotionStretchProperties(Actor& actor)
39 actor.RegisterProperty("uGeometryStretchFactor", 0.5f);
40 actor.RegisterProperty("uSpeedScalingFactor", 0.5f);
41 actor.RegisterProperty("uObjectFadeStart", Vector2(0.25f, 0.25f));
42 actor.RegisterProperty("uObjectFadeEnd", Vector2(0.5f, 0.5f));
43 actor.RegisterProperty("uAlphaScale", 0.75f);
44 Property::Index uModelProperty = actor.RegisterProperty("uModelLastFrame", Matrix::IDENTITY);
46 Constraint constraint = Constraint::New<Matrix>(actor, uModelProperty, EqualToConstraint());
47 constraint.AddSource(Source(actor, Actor::Property::WORLD_MATRIX));
52 * @brief Creates a new MotionStretchEffect
54 * Motion stretch shader works on a per object basis. Objects will stretch in the direction of motion when they move, or if the camera moves.
56 * Animatable/Constrainable uniforms:
57 * "uGeometryStretchFactor" - This scales the amount the geometry stretches along the motion velocity vector.
58 * A smaller value means the geometry stretches less, larger it stretches more. Default 0.5.
59 * "uSpeedScalingFactor" - This value is used to control how much to fade the actor near the edges, based on the
60 * speed the actor is moving. When the actor is at rest this is not applied. Default 0.5.
61 * "uObjectFadeStart" - The displacement from the centre of the actor that the actor will start to fade towards
62 * its edges. This is used to prevent an unsightly hard edge between the stretched actor and
63 * the scene. Depends on the values of the vertices in the vertex stream. When the actor is at
64 * rest this is not applied. Default Vector2(0.25, 0.25), which is half way towards the edge for
65 * an ImageVisual::QUAD.
66 * "uObjectFadeEnd" - The displacement from the centre of the actor that the actor will finish fading towards its edges.
67 * This is used to prevent an unsightly hard edge between the stretched actor and the scene. Depends
68 * on the values of the vertices in the vertex stream. When the actor is at rest this is not applied.
69 * Default 0.5, which is all the way towards the edge for an ImageVisual::QUAD.
70 * "uAlphaScale" - Global scaler applied to the alpha of the actor. Used to make the stretched actor a bit more subtle
71 * and reveal a bit of the background behind it as it moves. When the actor is at rest this is not
72 * applied. Default 0.75.
73 * "uModelLastFrame" - The model to world space transformation matrix of the actor in the previous frame.
75 * @return The newly created Property::Map with the motion stretch effect
77 inline Property::Map CreateMotionStretchEffect()
79 std::string vertexSource;
81 "precision mediump float;\n"
83 "attribute vec2 aPosition;\n"
85 "uniform mat4 uMvpMatrix;\n"
86 "uniform mat4 uModelView;\n"
87 "uniform mat4 uViewMatrix;\n"
88 "uniform mat4 uProjection;\n"
89 "uniform vec3 uSize;\n"
91 "uniform mat4 uModelLastFrame;\n"
92 "float timeDelta = 0.0167;\n"
94 "uniform float uGeometryStretchFactor;\n"
95 "uniform float uSpeedScalingFactor;\n"
98 "varying vec2 vModelSpaceCenterToPos;\n"
99 "varying vec2 vScreenSpaceVelocityVector;\n"
100 "varying float vSpeed;\n"
101 "varying vec2 vTexCoord;\n"
105 // get view space position of vertex this frame and last frame
106 " vec4 vertexPosition = vec4(aPosition, 0.0, 1.0);\n"
107 " vertexPosition.xyz *= uSize;\n"
109 " vec4 viewSpaceVertex = uModelView * vertexPosition;\n"
110 " vec4 viewSpaceVertexLastFrame = uViewMatrix * uModelLastFrame * vertexPosition;\n"
112 // work out vertex's last movement in view space
113 " vec3 viewSpacePosDelta = viewSpaceVertex.xyz - viewSpaceVertexLastFrame.xyz;\n"
114 " float reciprocalTimeDelta = 1.0 / timeDelta;\n"
116 // get clip space position of vertex this frame and last frame
117 " vec4 clipSpaceVertex = uMvpMatrix * vertexPosition;\n"
118 " vec4 clipSpaceVertexLastFrame = uProjection * viewSpaceVertexLastFrame;\n"
120 // decide how much this vertex is 'trailing', i.e. at the back of the object relative to its direction of motion. We do this
121 // by assuming the objects model space origin is at its center and taking the dot product of the vector from center to vertex with the motion direction
123 " float posDeltaLength = length(viewSpacePosDelta);\n"
124 " if(posDeltaLength > 0.001)\n" // avoid div by 0 if object has barely moved
126 " vec4 viewSpaceCenterToPos = uModelView * vec4(aPosition, 0.0, 0.0);\n"
127 " float centerToVertexDist = length(viewSpaceCenterToPos);\n"
128 " if(centerToVertexDist > 0.001)\n" // avoid div by 0 if object has vertex at model space origin
130 " vec3 viewSpacePosDeltaNormalised = viewSpacePosDelta / posDeltaLength;\n"
131 " vec3 viewSpaceCenterToPosNormalised = viewSpaceCenterToPos.xyz / centerToVertexDist;\n"
132 " t = (dot(viewSpacePosDeltaNormalised, viewSpaceCenterToPosNormalised) * 0.5 ) + 0.5;\n" // scale and bias from [-1..1] to [0..1]
135 // output vertex position lerped with its last position, based on how much it is trailing,
136 // this stretches the geom back along where it has just been, giving a warping effect
137 // We raise t to a power in order that non-trailing vertices are effected much more than trailing ones
138 // Note: we must take account of time delta to convert position delta into a velocity, so changes are smooth (take into account frame time correctly)
139 " gl_Position = mix(clipSpaceVertexLastFrame, clipSpaceVertex, t * t * t * uGeometryStretchFactor * reciprocalTimeDelta);\n"
141 // work out vertex's last movement in normalised device coordinates [-1..1] space, i.e. perspective divide
142 " vec2 ndcVertex = clipSpaceVertex.xy / clipSpaceVertex.w;\n"
143 " vec2 ndcVertexLastFrame = clipSpaceVertexLastFrame.xy / clipSpaceVertexLastFrame.w;\n"
144 // scale and bias so that a value of 1.0 corresponds to screen size (NDC is [-1..1] = 2)
145 " vScreenSpaceVelocityVector = ((ndcVertex - ndcVertexLastFrame) * 0.5 * reciprocalTimeDelta);\n"
146 " vScreenSpaceVelocityVector.y = -vScreenSpaceVelocityVector.y;\n" // TODO negated due to y being inverted in our coordinate system?
147 // calculate a scaling factor proportional to velocity, which we can use to tweak how things look
148 " vSpeed = length(vScreenSpaceVelocityVector) * uSpeedScalingFactor;\n"
149 " vSpeed = clamp(vSpeed, 0.0, 1.0);\n"
151 // provide fragment shader with vector from center of object to pixel (assumes the objects model space origin is at its center and verts have same z)
152 " vModelSpaceCenterToPos = viewSpaceVertex.xy;\n"
154 " vec2 texCoord = aPosition + vec2(0.5);"
155 " vTexCoord = texCoord;\n"
158 std::string fragmentSource;
160 "precision mediump float;\n"
162 "uniform sampler2D sTexture;\n"
163 "uniform vec4 uColor;\n"
165 "uniform vec2 uObjectFadeStart;\n"
166 "uniform vec2 uObjectFadeEnd;\n"
167 "uniform float uAlphaScale;\n"
170 "varying vec2 vModelSpaceCenterToPos;\n"
171 "varying vec2 vScreenSpaceVelocityVector;\n"
172 "varying float vSpeed;\n"
173 "varying vec2 vTexCoord;\n"
177 // calculate an alpha value that will fade the object towards its extremities, we need this to avoid an unsightly hard edge between color values of
178 // the stretched object and the background. Use smoothstep also to hide any hard edges (discontinuities) in rate of change of this alpha gradient
179 " vec2 centerToPixel = abs( vModelSpaceCenterToPos );\n"
180 " vec2 fadeToEdges = smoothstep(0.0, 1.0, 1.0 - ((centerToPixel - uObjectFadeStart) / (uObjectFadeEnd - uObjectFadeStart)));\n"
181 " float fadeToEdgesScale = fadeToEdges.x * fadeToEdges.y * uAlphaScale;\n" // apply global scaler
182 " fadeToEdgesScale = mix(1.0, fadeToEdgesScale, vSpeed);\n" // fade proportional to speed, so opaque when at rest
184 // standard actor texel
185 " vec4 colActor = texture2D(sTexture, vTexCoord);\n"
186 " gl_FragColor = colActor;\n"
187 " gl_FragColor.a *= fadeToEdgesScale;\n" // fade actor to its edges based on speed of motion
188 " gl_FragColor *= uColor;\n"
193 Property::Map customShader;
194 customShader[Visual::Shader::Property::VERTEX_SHADER] = vertexSource;
195 customShader[Visual::Shader::Property::FRAGMENT_SHADER] = fragmentSource;
197 customShader[Visual::Shader::Property::SUBDIVIDE_GRID_X] = 10;
198 customShader[Visual::Shader::Property::SUBDIVIDE_GRID_Y] = 10;
200 customShader[Visual::Shader::Property::HINTS] = Shader::Hint::OUTPUT_IS_TRANSPARENT;
202 map[Toolkit::Visual::Property::SHADER] = customShader;
206 } // namespace Toolkit
210 #endif // DALI_TOOLKIT_SHADER_EFFECT_MOTION_STRETCH_H