1 #ifndef __DALI_TOOLKIT_SHADER_EFFECT_MOTION_STRETCH_H__
2 #define __DALI_TOOLKIT_SHADER_EFFECT_MOTION_STRETCH_H__
5 * Copyright (c) 2015 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/image-actor.h>
23 #include <dali/public-api/shader-effects/shader-effect.h>
32 * @brief Set the properties for the motion stretch
34 inline void SetMotionStretchProperties( Actor& actor )
36 actor.RegisterProperty( "uGeometryStretchFactor", 0.5f );
37 actor.RegisterProperty( "uSpeedScalingFactor", 0.5f );
38 actor.RegisterProperty( "uObjectFadeStart", Vector2( 0.25f, 0.25f ) );
39 actor.RegisterProperty( "uObjectFadeEnd", Vector2( 0.5f, 0.5f ) );
40 actor.RegisterProperty( "uAlphaScale", 0.75f );
41 Property::Index uModelProperty = actor.RegisterProperty( "uModelLastFrame", Matrix::IDENTITY );
43 Constraint constraint = Constraint::New<Matrix>( actor, uModelProperty, EqualToConstraint() );
44 constraint.AddSource( Source( actor , Actor::Property::WORLD_MATRIX ) );
49 * @brief Creates a new MotionStretchEffect
51 * 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.
53 * Animatable/Constrainable uniforms:
54 * "uGeometryStretchFactor" - This scales the amount the geometry stretches along the motion velocity vector.
55 * A smaller value means the geometry stretches less, larger it stretches more. Default 0.5.
56 * "uSpeedScalingFactor" - This value is used to control how much to fade the actor near the edges, based on the
57 * speed the actor is moving. When the actor is at rest this is not applied. Default 0.5.
58 * "uObjectFadeStart" - The displacement from the centre of the actor that the actor will start to fade towards
59 * its edges. This is used to prevent an unsightly hard edge between the stretched actor and
60 * the scene. Depends on the values of the vertices in the vertex stream. When the actor is at
61 * rest this is not applied. Default Vector2(0.25, 0.25), which is half way towards the edge for
62 * an ImageRenderer::QUAD.
63 * "uObjectFadeEnd" - The displacement from the centre of the actor that the actor will finish fading towards its edges.
64 * This is used to prevent an unsightly hard edge between the stretched actor and the scene. Depends
65 * on the values of the vertices in the vertex stream. When the actor is at rest this is not applied.
66 * Default 0.5, which is all the way towards the edge for an ImageRenderer::QUAD.
67 * "uAlphaScale" - Global scaler applied to the alpha of the actor. Used to make the stretched actor a bit more subtle
68 * and reveal a bit of the background behind it as it moves. When the actor is at rest this is not
69 * applied. Default 0.75.
70 * "uModelLastFrame" - The model to world space transformation matrix of the actor in the previous frame.
72 * @return The newly created Property::Map with the motion stretch effect
74 inline Property::Map CreateMotionStretchEffect()
76 std::string vertexSource;
78 "precision mediump float;\n"
80 "attribute vec2 aPosition;\n"
82 "uniform mat4 uMvpMatrix;\n"
83 "uniform mat4 uModelView;\n"
84 "uniform mat4 uViewMatrix;\n"
85 "uniform mat4 uProjection;\n"
86 "uniform vec3 uSize;\n"
88 "uniform mat4 uModelLastFrame;\n"
89 "float timeDelta = 0.0167;\n"
91 "uniform float uGeometryStretchFactor;\n"
92 "uniform float uSpeedScalingFactor;\n"
95 "varying vec2 vModelSpaceCenterToPos;\n"
96 "varying vec2 vScreenSpaceVelocityVector;\n"
97 "varying float vSpeed;\n"
98 "varying vec2 vTexCoord;\n"
102 // get view space position of vertex this frame and last frame
103 " vec4 vertexPosition = vec4(aPosition, 0.0, 1.0);\n"
104 " vertexPosition.xyz *= uSize;\n"
106 " vec4 viewSpaceVertex = uModelView * vertexPosition;\n"
107 " vec4 viewSpaceVertexLastFrame = uViewMatrix * uModelLastFrame * vertexPosition;\n"
109 // work out vertex's last movement in view space
110 " vec3 viewSpacePosDelta = viewSpaceVertex.xyz - viewSpaceVertexLastFrame.xyz;\n"
111 " float reciprocalTimeDelta = 1.0 / timeDelta;\n"
113 // get clip space position of vertex this frame and last frame
114 " vec4 clipSpaceVertex = uMvpMatrix * vertexPosition;\n"
115 " vec4 clipSpaceVertexLastFrame = uProjection * viewSpaceVertexLastFrame;\n"
117 // decide how much this vertex is 'trailing', i.e. at the back of the object relative to its direction of motion. We do this
118 // 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
120 " float posDeltaLength = length(viewSpacePosDelta);\n"
121 " if(posDeltaLength > 0.001)\n" // avoid div by 0 if object has barely moved
123 " vec4 viewSpaceCenterToPos = uModelView * vec4(aPosition, 0.0, 0.0);\n"
124 " float centerToVertexDist = length(viewSpaceCenterToPos);\n"
125 " if(centerToVertexDist > 0.001)\n" // avoid div by 0 if object has vertex at model space origin
127 " vec3 viewSpacePosDeltaNormalised = viewSpacePosDelta / posDeltaLength;\n"
128 " vec3 viewSpaceCenterToPosNormalised = viewSpaceCenterToPos.xyz / centerToVertexDist;\n"
129 " t = (dot(viewSpacePosDeltaNormalised, viewSpaceCenterToPosNormalised) * 0.5 ) + 0.5;\n" // scale and bias from [-1..1] to [0..1]
132 // output vertex position lerped with its last position, based on how much it is trailing,
133 // this stretches the geom back along where it has just been, giving a warping effect
134 // We raise t to a power in order that non-trailing vertices are effected much more than trailing ones
135 // 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)
136 " gl_Position = mix(clipSpaceVertexLastFrame, clipSpaceVertex, t * t * t * uGeometryStretchFactor * reciprocalTimeDelta);\n"
138 // work out vertex's last movement in normalised device coordinates [-1..1] space, i.e. perspective divide
139 " vec2 ndcVertex = clipSpaceVertex.xy / clipSpaceVertex.w;\n"
140 " vec2 ndcVertexLastFrame = clipSpaceVertexLastFrame.xy / clipSpaceVertexLastFrame.w;\n"
141 // scale and bias so that a value of 1.0 corresponds to screen size (NDC is [-1..1] = 2)
142 " vScreenSpaceVelocityVector = ((ndcVertex - ndcVertexLastFrame) * 0.5 * reciprocalTimeDelta);\n"
143 " vScreenSpaceVelocityVector.y = -vScreenSpaceVelocityVector.y;\n" // TODO negated due to y being inverted in our coordinate system?
144 // calculate a scaling factor proportional to velocity, which we can use to tweak how things look
145 " vSpeed = length(vScreenSpaceVelocityVector) * uSpeedScalingFactor;\n"
146 " vSpeed = clamp(vSpeed, 0.0, 1.0);\n"
148 // 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)
149 " vModelSpaceCenterToPos = viewSpaceVertex.xy;\n"
151 " vec2 texCoord = aPosition + vec2(0.5);"
152 " vTexCoord = texCoord;\n"
155 std::string fragmentSource;
157 "precision mediump float;\n"
159 "uniform sampler2D sTexture;\n"
160 "uniform vec4 uColor;\n"
162 "uniform vec2 uObjectFadeStart;\n"
163 "uniform vec2 uObjectFadeEnd;\n"
164 "uniform float uAlphaScale;\n"
167 "varying vec2 vModelSpaceCenterToPos;\n"
168 "varying vec2 vScreenSpaceVelocityVector;\n"
169 "varying float vSpeed;\n"
170 "varying vec2 vTexCoord;\n"
174 // 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
175 // the stretched object and the background. Use smoothstep also to hide any hard edges (discontinuities) in rate of change of this alpha gradient
176 " vec2 centerToPixel = abs( vModelSpaceCenterToPos );\n"
177 " vec2 fadeToEdges = smoothstep(0.0, 1.0, 1.0 - ((centerToPixel - uObjectFadeStart) / (uObjectFadeEnd - uObjectFadeStart)));\n"
178 " float fadeToEdgesScale = fadeToEdges.x * fadeToEdges.y * uAlphaScale;\n" // apply global scaler
179 " fadeToEdgesScale = mix(1.0, fadeToEdgesScale, vSpeed);\n" // fade proportional to speed, so opaque when at rest
181 // standard actor texel
182 " vec4 colActor = texture2D(sTexture, vTexCoord);\n"
183 " gl_FragColor = colActor;\n"
184 " gl_FragColor.a *= fadeToEdgesScale;\n" // fade actor to its edges based on speed of motion
185 " gl_FragColor *= uColor;\n"
190 Property::Map customShader;
191 customShader[ "vertexShader" ] = vertexSource;
192 customShader[ "fragmentShader" ] = fragmentSource;
194 customShader[ "subdivideGridX" ] = 10;
195 customShader[ "subdivideGridY" ] = 10;
197 // NOTE: we must turn on alpha blending for the actor (HINT_BLENDING)
198 customShader[ "hints" ] = "outputIsTransparent";
200 map[ "shader" ] = customShader;
208 #endif //#ifndef __DALI_TOOLKIT_SHADER_EFFECT_MOTION_STRETCH_H__