使用opengl做的粒子系统有些问题，求大神指教

云络 2018-11-02 03:59:55

下图效果是使用粒子系统生成的，我感觉红框里面的两个红包相互影响了，但是有一些又不会有影响，求大神指出问题所在

红包的原图是这个，除了中间的红包，其余透明度都为0，因为工程需要，所以透明度为0的部分不能裁剪掉

绘制的流程比较简单，就是使用几何着色器去生成顶点和UV，再在片段着色器中绘制，下面是几何着色器的部分代码：

out vec2 UV;

out vec4 color;

//获取相机坐标系中的坐标

vec4 GetLocalCoord(vec3 position)

{

    vec4 view_coord = view_matrix * particle_model_matrix * vec4(position, 1);

    return view_coord;

}



//DrawRectangle根据当前输入的点的坐标计算矩形的四个顶点坐标以及uv

void DrawRectangle(vec3 center_position, float size, float ratio)

{

    color = particle[0].color;

    color.a = particle[0].opacity;

    

    float width_half_size = size / 2;

    float height_half_size = width_half_size / ratio;

    vec4 local_coord = GetLocalCoord(center_position);

    local_coord.x = local_coord.x / local_coord.a;

    local_coord.y = local_coord.y / local_coord.a;

    local_coord.z = local_coord.z / local_coord.a;

    local_coord.a = 0;



    vec4 top_left = vec4(-width_half_size, height_half_size, 0.0, 1.0);

    vec4 top_right = vec4(width_half_size, height_half_size, 0.0, 1.0);

    vec4 bottom_left = vec4(-width_half_size, -height_half_size, 0.0, 1.0);

    vec4 bottom_right = vec4(width_half_size, -height_half_size, 0.0, 1.0);



    vec4 top_left_rotate = particle[0].rotation_matrix * top_left;

    vec4 top_right_rotate = particle[0].rotation_matrix * top_right;

    vec4 bottom_left_rotate = particle[0].rotation_matrix * bottom_left;

    vec4 bottom_right_rotate = particle[0].rotation_matrix * bottom_right;



    top_left_rotate = vec4(top_left_rotate.x / top_left_rotate.a, top_left_rotate.y / top_left_rotate.a, 0.0, 1.0) + local_coord;

    top_right_rotate = vec4(top_right_rotate.x / top_right_rotate.a, top_right_rotate.y / top_right_rotate.a, 0.0, 1.0) + local_coord;

    bottom_left_rotate = vec4(bottom_left_rotate.x / bottom_left_rotate.a, bottom_left_rotate.y / bottom_left_rotate.a, 0.0, 1.0) + local_coord;

    bottom_right_rotate = vec4(bottom_right_rotate.x / bottom_right_rotate.a, bottom_right_rotate.y / bottom_right_rotate.a, 0.0, 1.0) + local_coord;



    vec4 top_left_screen = projection_matrix * top_left_rotate;

    vec4 top_right_screen = projection_matrix * top_right_rotate;

    vec4 bottom_left_screen = projection_matrix * bottom_left_rotate;

    vec4 bottom_right_screen = projection_matrix * bottom_right_rotate;



    UV = vec2(0.0, 1.0);

    gl_Position = top_left_screen;

    EmitVertex();



    UV = vec2(1.0, 1.0);

    gl_Position = top_right_screen;

    EmitVertex();



    UV = vec2(0, 0);

    gl_Position = bottom_left_screen;

    EmitVertex();



    UV = vec2(1.0, 0);

    gl_Position = bottom_right_screen;

    EmitVertex();

    EndPrimitive();

}

下面是片段着色器中的代码：



uniform sampler2D framebuffer_sampler;

uniform sampler2D particle_texture;

uniform int blend_mode;

uniform bool is_use_texture = false;

uniform vec2 resolution = vec2(720, 1080);



in vec2 UV;

in vec4 color;

out vec4 Frag_Color;



void DoBlend()

{

  float src_luma = Frag_Color.r * Frag_Color.a;

  float src_alpha = Frag_Color.a;



  vec2 p = gl_FragCoord.xy / resolution.xy;

  vec4 frame_buffer_color = texture(framebuffer_sampler, p);

  vec4 src_cor = Frag_Color; //top color

  vec4 dst_cor = frame_buffer_color; //base color

  vec3 blend_color = vec3(0.0);

  float result_alpha = src_cor.a + (1 - src_cor.a)*dst_cor.a;

  switch (blend_mode)

  {

    case 0: 

        blend_color = src_cor.rgb;

        break;

    case 1: 

        blend_color = src_cor.rgb + dst_cor.rgb;

        break;

    case 19: 

        blend_color = max(src_cor.rgb, dst_cor.rgb);

        break;

    case 30: 

        blend_color = src_cor.rgb + dst_cor.rgb - (src_cor.rgb * dst_cor.rgb);

        break;

    default:

        blend_color = src_cor.rgb;

        break;

  }

  if (result_alpha != 0)

    Frag_Color.rgb = (1 - src_cor.a/result_alpha)*dst_cor.rgb + (src_cor.a/result_alpha)*((1 - dst_cor.a)*src_cor.rgb + dst_cor.a * blend_color);

  else

    Frag_Color.rgb = blend_color;



  Frag_Color.a = result_alpha;

}



void main()

{

        Frag_Color = texture(particle_texture, UV);

        Frag_Color.a = color.a * Frag_Color.a;

        DoBlend();

}