Setting highlight to an image in OpenGL shader language - opengl

Question

I'm trying to set a highlight mask to an image currently covered by mouse. My problem is that instead of setting the mask to all corners of an image it sets it only to the left top corner.
Here are my shaders:
string vertexShaderSource = #"
#version 140
uniform mat4 modelview_matrix;
uniform mat4 projection_matrix;
// incoming
in vec3 vertex_position;
in vec2 i_texCoord;
in vec4 i_highlightColor;
//outgoing
out vec2 o_texCoord;
out vec4 o_highlightColor;
void main(void)
{
gl_Position = projection_matrix * modelview_matrix * vec4( vertex_position, 1 );
o_texCoord = i_texCoord;
o_highlightColor = i_highlightColor;
}";
string fragmentShaderSource = #"
#version 140
precision highp float;
in vec2 o_texCoord;
in vec4 o_highlightColor;
out vec4 out_frag_color;
uniform sampler2D s_texture;
void main(void)
{
out_frag_color = texture( s_texture, o_texCoord ) + o_highlightColor;
if(out_frag_color.a == 0.0)
discard;
}";
This is how I transfer the highlight color to the graphics card:
float[] highlightColor = new float[myList.Count * 4];
int count = 0;
float[] noHighlight = new float[4] { 0.0f, 0.0f, 0.0f, 0.0f };
float[] yesHighlight = new float[4] { 1.0f, 0.0f, 0.0f, 0.3f };
foreach (GameObject go in myList)
{
...
for (int i = 0; i < 4; i++)
{
if (go.currentlyHovered)
highlightColor[count * 4 + i] = yesHighlight[i];
else
highlightColor[count * 4 + i] = noHighlight[i];
}
...
count++;
}
...
GL.BindBuffer(BufferTarget.ArrayBuffer, highlightColorLocation);
GL.BufferData<float>(BufferTarget.ArrayBuffer,
new IntPtr(highlightColor.Length * sizeof(float)),
highlightColor, BufferUsageHint.StaticDraw);
GL.EnableVertexAttribArray(2);
GL.BindAttribLocation(shaderProgramHandle, 2, "i_highlightColor");
GL.VertexAttribPointer(2, 4, VertexAttribPointerType.Float, false, OpenTK.Vector4.SizeInBytes, 0);
...
It seems as if I'm sending the highlight color only to one vertex but why? I thought the "in" modifier in glsl causes that data is sent to every vertex... And interesting is fact that when I replace "+ o_highlightColor" in my fargment shader with " + vec4(1.0, 0.0, 0.0, 0.3)" then the lighting covers whole image!

Answer 1

It seems like I've overlooked the fact that in order to apply the highlight to whole quad I need to send the highlight data to all 4 vertices, not only one like above. In total it will be 16 floats per object in each render frame in order to apply consistent highlight on whole area of the object.
float[] highlightColor = new float[myList.Count * 16];
int count = 0;
float[] noHighlight = new float[4] { 0.0f, 0.0f, 0.0f, 0.0f };
float[] yesHighlight = new float[4] { 1.0f, 0.0f, 0.0f, 0.3f };
foreach (GameObject go in myList)
{
...
for (int i = 0; i < 16; i++)
{
if (go.currentlyHovered)
highlightColor[count * 16 + i] = yesHighlight[i % 4];
else
highlightColor[count * 16 + i] = noHighlight[i % 4];
}
...
count++;
}