[#69] Additively blend particles and make them look rounded

include/vkcv/PipelineConfig.hpp

@@ -15,6 +15,10 @@ namespace vkcv {
 
     enum class PrimitiveTopology{PointList, LineList, TriangleList };
 
+    // add more as needed
+    // alternatively we could expose the blend factors directly
+    enum class BlendMode{ None, Additive };
+
     struct PipelineConfig {
         ShaderProgram                         m_ShaderProgram;
         uint32_t                              m_Width;
@@ -25,6 +29,7 @@ namespace vkcv {
         bool                                  m_UseDynamicViewport;
         bool                                  m_UseConservativeRasterization = false;
         PrimitiveTopology                     m_PrimitiveTopology = PrimitiveTopology::TriangleList;
+        BlendMode                             m_blendMode = BlendMode::None;
     };
 
 }
\ No newline at end of file

projects/particle_simulation/shaders/particleShading.inc

+float circleFactor(vec2 triangleCoordinates){
+    // percentage of distance from center to circle edge
+    float p = clamp((0.4 - length(triangleCoordinates)) / 0.4, 0, 1);
+    // remapping for nice falloff
+    return sqrt(p);
+}
\ No newline at end of file

projects/particle_simulation/shaders/shader.vert

@@ -23,6 +23,7 @@ layout( push_constant ) uniform constants{
     mat4 projection;
 };
 
+layout(location = 0) out vec2 passTriangleCoordinates;
 layout(location = 1) out vec3 passVelocity;
 layout(location = 2) out float passlifeTime;
 
@@ -36,5 +37,9 @@ void main()
     // by adding the triangle position in view space the mesh is always camera facing
     positionView.xyz += particle;
     // multiply with projection matrix for final position
-	gl_Position =   projection * positionView;
+	gl_Position = projection * positionView;
+    
+    // 0.01 corresponds to vertex position size in main
+    float normalizationDivider  = 0.01;
+    passTriangleCoordinates     = particle.xy / normalizationDivider;
 }
\ No newline at end of file

projects/particle_simulation/shaders/shader_space.frag

 #version 450
 #extension GL_ARB_separate_shader_objects : enable
+#extension GL_GOOGLE_include_directive : enable
 
+#include "particleShading.inc"
+
+layout(location = 0) in vec2 passTriangleCoordinates;
 layout(location = 1) in vec3 passVelocity;
 layout(location = 2) in float passlifeTime;
 
@@ -14,6 +18,7 @@ layout(set=0,binding=1) uniform uPosition{
 	vec2 position;
 } Position;
 
+
 void main()
 {
 	vec2 mouse = vec2(Position.position.x, Position.position.y);
@@ -21,4 +26,9 @@ void main()
 				   float(passlifeTime < 2 && passlifeTime > 1) * vec4(1,passlifeTime * 0.5,0,0) +
 				   float(passlifeTime >= 2 && passlifeTime < 2.5f) * vec4(passlifeTime * 0.5,passlifeTime * 0.5,0,0) +
 				   float(passlifeTime >= 2.5f) * vec4(1,0,0,0);
+   
+   // make the triangle look like a circle
+   outColor *= circleFactor(passTriangleCoordinates);
+   // full color is achieved by additively blending many particles
+   outColor *= 0.5; 
 }
\ No newline at end of file

projects/particle_simulation/shaders/shader_water.frag

 #version 450
 #extension GL_ARB_separate_shader_objects : enable
+#extension GL_GOOGLE_include_directive : enable
 
+#include "particleShading.inc"
+
+layout(location = 0) in vec2 passTriangleCoordinates;
 layout(location = 1) in vec3 passVelocity;
 layout(location = 2) in float passlifeTime;
 
@@ -22,4 +26,9 @@ void main()
 	float(passlifeTime < 2 && passlifeTime > 1) * vec4(0.3, 0.7,1,0) +
 	float(passlifeTime >= 2 && passlifeTime < 4.f) * vec4(0.5,0.9,1,0) +
 	float(passlifeTime >= 4.f) * vec4(0.9,1,1,0);
+    
+    // make the triangle look like a circle
+   outColor *= circleFactor(passTriangleCoordinates);
+   // full color is achieved by additively blending many particles
+   outColor *= 0.5; 
 }

projects/particle_simulation/src/main.cpp

@@ -95,7 +95,7 @@ int main(int argc, const char **argv) {
 
     const vkcv::VertexLayout particleLayout(bindings);
 
-    const vkcv::PipelineConfig particlePipelineDefinition{
+    vkcv::PipelineConfig particlePipelineDefinition{
             particleShaderProgram,
             UINT32_MAX,
             UINT32_MAX,
@@ -103,10 +103,11 @@ int main(int argc, const char **argv) {
             {particleLayout},
             {core.getDescriptorSet(descriptorSet).layout},
             true};
+    particlePipelineDefinition.m_blendMode = vkcv::BlendMode::Additive;
 
-    const std::vector<glm::vec3> vertices = {glm::vec3(-0.005, 0.005, 0),
-                                             glm::vec3(0.005, 0.005, 0),
-                                             glm::vec3(0, -0.005, 0)};
+    const std::vector<glm::vec3> vertices = {glm::vec3(-0.01, 0.01, 0),
+                                             glm::vec3(0.01, 0.01, 0),
+                                             glm::vec3(0, -0.01, 0)};
 
     vertexBuffer.fill(vertices);
 

src/vkcv/PipelineManager.cpp

@@ -182,8 +182,11 @@ namespace vkcv
                                                VK_COLOR_COMPONENT_G_BIT |
                                                VK_COLOR_COMPONENT_B_BIT |
                                                VK_COLOR_COMPONENT_A_BIT);
+
+        // currently set to additive, if not disabled
+        // BlendFactors must be set as soon as additional BlendModes are added
         vk::PipelineColorBlendAttachmentState colorBlendAttachmentState(
-                false,
+                config.m_blendMode != BlendMode::None,
                 vk::BlendFactor::eOne,
                 vk::BlendFactor::eOne,
                 vk::BlendOp::eAdd,