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 Creates a new MotionStretchEffect
34 * 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. Can be applied
35 * to ImageActor or TextActor only.
39 * // Create shader used for doing motion stretch\n
40 * ShaderEffect MotionStretchEffect = CreateMotionStretchEffect();
42 * // set actor shader to the stretch one\n
43 * Actor actor = Actor::New( ... );\n
44 * actor.SetShaderEffect( MotionStretchEffect );
46 * // Constrain "uModelLastFrame" to be the same as the actor's world matrix\n
47 * Dali::Property::Index uModelProperty = MotionBlurEffect.GetPropertyIndex( "uModelLastFrame" );
48 * Constraint constraint = Constraint::New<Matrix>( MotionBlurEffect, uModelProperty, EqualToConstraint() );\n
49 * constraint.AddSource( Source( actor , Actor::Property::WORLD_MATRIX ) );\n
50 * constraint.Apply();\n
52 * Animatable/Constrainable uniforms:
53 * "uGeometryStretchFactor" - This scales the amount the geometry stretches along the motion velocity vector.
54 * A smaller value means the geometry stretches less, larger it stretches more. Default 0.5.
55 * "uSpeedScalingFactor" - This value is used to control how much to fade the actor near the edges, based on the
56 * speed the actor is moving. When the actor is at rest this is not applied. Default 0.5.
57 * "uObjectFadeStart" - The displacement from the centre of the actor that the actor will start to fade towards
58 * its edges. This is used to prevent an unsightly hard edge between the stretched actor and
59 * the scene. Depends on the values of the vertices in the vertex stream. When the actor is at
60 * rest this is not applied. Default Vector2(0.25, 0.25), which is half way towards the edge for
61 * an ImageRenderer::QUAD.
62 * "uObjectFadeEnd" - The displacement from the centre of the actor that the actor will finish fading towards its edges.
63 * This is used to prevent an unsightly hard edge between the stretched actor and the scene. Depends
64 * on the values of the vertices in the vertex stream. When the actor is at rest this is not applied.
65 * Default 0.5, which is all the way towards the edge for an ImageRenderer::QUAD.
66 * "uAlphaScale" - Global scaler applied to the alpha of the actor. Used to make the stretched actor a bit more subtle
67 * and reveal a bit of the background behind it as it moves. When the actor is at rest this is not
68 * applied. Default 0.75.
69 * "uModelLastFrame" - The model to world space transformation matrix of the actor in the previous frame.
71 * @return A handle to a newly allocated ShaderEffect
73 inline ShaderEffect CreateMotionStretchEffect()
75 // Dali vertexSource prefix for reference:
76 // precision highp float;
77 // attribute vec3 aPosition;
78 // attribute vec2 aTexCoord;
79 // uniform mat4 uMvpMatrix;
80 // uniform mat4 uModelView;
81 // uniform mat3 uNormalMatrix;
82 // uniform mat4 uProjection;
83 // uniform vec4 uColor;
84 // varying vec2 vTexCoord;
85 std::string vertexSource;
87 "precision mediump float;\n"
88 "uniform mat4 uModelLastFrame;\n"
89 "uniform float uTimeDelta;\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"
101 // get view space position of vertex this frame and last frame
102 " vec4 vertex = vec4(aPosition, 1.0);\n"
103 " vec4 viewSpaceVertex = uModelView * vertex;\n"
104 " vec4 viewSpaceVertexLastFrame = uViewMatrix * uModelLastFrame * vertex;\n"
106 // work out vertex's last movement in view space
107 " vec3 viewSpacePosDelta = viewSpaceVertex.xyz - viewSpaceVertexLastFrame.xyz;\n"
108 " float reciprocalTimeDelta = 1.0 / ((uTimeDelta > 0.0) ? uTimeDelta : 0.01);\n"
110 // get clip space position of vertex this frame and last frame
111 " vec4 clipSpaceVertex = uMvpMatrix * vertex;\n"
112 " vec4 clipSpaceVertexLastFrame = uProjection * viewSpaceVertexLastFrame;\n"
114 // decide how much this vertex is 'trailing', i.e. at the back of the object relative to its direction of motion. We do this
115 // 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
117 " float posDeltaLength = length(viewSpacePosDelta);\n"
118 " if(posDeltaLength > 0.001)\n" // avoid div by 0 if object has barely moved
120 " vec4 viewSpaceCenterToPos = uModelView * vec4(aPosition, 0.0);\n"
121 " float centerToVertexDist = length(viewSpaceCenterToPos);\n"
122 " if(centerToVertexDist > 0.001)\n" // avoid div by 0 if object has vertex at model space origin
124 " vec3 viewSpacePosDeltaNormalised = viewSpacePosDelta / posDeltaLength;\n"
125 " vec3 viewSpaceCenterToPosNormalised = viewSpaceCenterToPos.xyz / centerToVertexDist;\n"
126 " t = (dot(viewSpacePosDeltaNormalised, viewSpaceCenterToPosNormalised) * 0.5 ) + 0.5;\n" // scale and bias from [-1..1] to [0..1]
129 // output vertex position lerped with its last position, based on how much it is trailing,
130 // this stretches the geom back along where it has just been, giving a warping effect
131 // We raise t to a power in order that non-trailing vertices are effected much more than trailing ones
132 // 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)
133 " gl_Position = mix(clipSpaceVertexLastFrame, clipSpaceVertex, t * t * t * uGeometryStretchFactor * reciprocalTimeDelta);\n"
135 // work out vertex's last movement in normalised device coordinates [-1..1] space, i.e. perspective divide
136 " vec2 ndcVertex = clipSpaceVertex.xy / clipSpaceVertex.w;\n"
137 " vec2 ndcVertexLastFrame = clipSpaceVertexLastFrame.xy / clipSpaceVertexLastFrame.w;\n"
138 // scale and bias so that a value of 1.0 corresponds to screen size (NDC is [-1..1] = 2)
139 " vScreenSpaceVelocityVector = ((ndcVertex - ndcVertexLastFrame) * 0.5 * reciprocalTimeDelta);\n"
140 " vScreenSpaceVelocityVector.y = -vScreenSpaceVelocityVector.y;\n" // TODO negated due to y being inverted in our coordinate system?
141 // calculate a scaling factor proportional to velocity, which we can use to tweak how things look
142 " vSpeed = length(vScreenSpaceVelocityVector) * uSpeedScalingFactor;\n"
143 " vSpeed = clamp(vSpeed, 0.0, 1.0);\n"
145 // 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)
146 " vModelSpaceCenterToPos = aPosition.xy;\n"
148 " vTexCoord = aTexCoord;\n"
152 // Dali fragmentSource prefix for reference:
153 // precision highp float;
154 // uniform sampler2D sTexture;
155 // uniform sampler2D sEffect;
156 // uniform vec4 uColor;
157 // varying vec2 vTexCoord;
158 std::string fragmentSource;
160 "precision mediump float;\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"
173 // 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
174 // the stretched object and the background. Use smoothstep also to hide any hard edges (discontinuities) in rate of change of this alpha gradient
175 " vec2 centerToPixel = abs( vModelSpaceCenterToPos );\n"
176 " vec2 fadeToEdges = smoothstep(0.0, 1.0, 1.0 - ((centerToPixel - uObjectFadeStart) / (uObjectFadeEnd - uObjectFadeStart)));\n"
177 " float fadeToEdgesScale = fadeToEdges.x * fadeToEdges.y * uAlphaScale;\n" // apply global scaler
178 " fadeToEdgesScale = mix(1.0, fadeToEdgesScale, vSpeed);\n" // fade proportional to speed, so opaque when at rest
180 // standard actor texel
181 " vec4 colActor = texture2D(sTexture, vTexCoord);\n"
182 " gl_FragColor = colActor;\n"
183 " gl_FragColor.a *= fadeToEdgesScale;\n" // fade actor to its edges based on speed of motion
184 " gl_FragColor *= uColor;\n"
187 // NOTE: we must turn on alpha blending for the actor (HINT_BLENDING)
188 ShaderEffect shaderEffect = ShaderEffect::New(
189 vertexSource, fragmentSource,
190 ShaderEffect::GeometryHints( ShaderEffect::HINT_BLENDING | ShaderEffect::HINT_GRID ) );
193 //////////////////////////////////////
194 // Register uniform properties
197 shaderEffect.SetUniform( "uGeometryStretchFactor", 0.5f );
198 shaderEffect.SetUniform( "uSpeedScalingFactor", 0.5f );
199 shaderEffect.SetUniform( "uObjectFadeStart", Vector2( 0.25f, 0.25f ) );
200 shaderEffect.SetUniform( "uObjectFadeEnd", Vector2( 0.5f, 0.5f ) );
201 shaderEffect.SetUniform( "uAlphaScale", 0.75f );
202 shaderEffect.SetUniform( "uModelLastFrame", Matrix::IDENTITY );
211 #endif //#ifndef __DALI_TOOLKIT_SHADER_EFFECT_MOTION_STRETCH_H__