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Line Stipple Shader #68

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Line Stipple Shader #68

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f7450bb
Create line_stipple.frag
Pranavya-Vivek Jul 24, 2023
d430343
Update shaders.qrc
Pranavya-Vivek Jul 24, 2023
d5472f2
Update material.cpp
Pranavya-Vivek Jul 24, 2023
dd73a16
Update material.h
Pranavya-Vivek Jul 24, 2023
2341f19
Update line_stipple.frag
Pranavya-Vivek Jul 25, 2023
7caca73
Convert Line-Stipple shader to geometric shader
Pranavya-Vivek Jul 27, 2023
1c130b9
Update shaders.qrc
Pranavya-Vivek Jul 27, 2023
2cc01b1
Update material.cpp
Pranavya-Vivek Jul 27, 2023
23cdd81
Update material.h
Pranavya-Vivek Jul 27, 2023
613f0b5
Update material.cpp
Pranavya-Vivek Aug 4, 2023
975aad0
Update material.h
Pranavya-Vivek Aug 4, 2023
ee619c0
Update shaders.qrc
Pranavya-Vivek Aug 4, 2023
c460193
Update widget.cpp
Pranavya-Vivek Aug 4, 2023
b810d3d
Update line_stipple.geom
Pranavya-Vivek Aug 4, 2023
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6 changes: 5 additions & 1 deletion src/material.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -71,6 +71,10 @@ RenderableMaterial::RenderableMaterial(Qt3DCore::QNode *parent, VertexShaderType
shader3->setFragmentShaderCode(
Qt3DRender::QShaderProgram::loadSource(QUrl(QStringLiteral("qrc:/shaders/shaders/monochrome.frag"))));
break;
case (FragmentShaderType::LineStipple):
shader3->setFragmentShaderCode(
Qt3DRender::QShaderProgram::loadSource(QUrl(QStringLiteral("qrc:/shaders/shaders/line_stipple.frag"))));
break;
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If the line stipple is to be a fragment shader then we would have to have a version for each type of colouring (e.g. Phong) we want to be "stipplable". Do we think this is the best approach?

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@Pranavya-Vivek Pranavya-Vivek Jul 25, 2023 •
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Okay yes! I think I can implement a similar approach to the line stippling code, but using a geometry shader instead. Then we would only need one geometry shader, regardless of how the lines are coloured. I'll add the updated commit here;

case (FragmentShaderType::Phong):
shader3->setFragmentShaderCode(
Qt3DRender::QShaderProgram::loadSource(QUrl(QStringLiteral("qrc:/shaders/shaders/phong.frag"))));
Expand Down Expand Up @@ -122,4 +126,4 @@ void RenderableMaterial::setSpecular(QColor specular)
{
specular_ = specular;
specularParameter_->setValue(specular_);
}
}
5 changes: 3 additions & 2 deletions src/material.h
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Original file line number Diff line number Diff line change
Expand Up @@ -26,7 +26,8 @@ class RenderableMaterial : public Qt3DRender::QMaterial
{
Monochrome,
Phong,
PerVertexPhong
PerVertexPhong,
LineStipple
};
explicit RenderableMaterial(Qt3DCore::QNode *parent, VertexShaderType vertexShader, GeometryShaderType geometryShader,
FragmentShaderType fragmentShader);
Expand Down Expand Up @@ -56,4 +57,4 @@ class RenderableMaterial : public Qt3DRender::QMaterial
// Set specular colour component
void setSpecular(QColor specular);
};
} // namespace Mildred
} // namespace Mildred
1 change: 1 addition & 0 deletions src/shaders.qrc
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@
<file>shaders/phong.frag</file>
<file>shaders/phongpervertex.frag</file>
<file>shaders/monochrome.frag</file>
<file>shaders/line_stipple.frag</file>
<file>shaders/line_tesselator.geom</file>
</qresource>
</RCC>
35 changes: 35 additions & 0 deletions src/shaders/line_stipple.frag
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Original file line number Diff line number Diff line change
@@ -0,0 +1,35 @@
#version 330 core

layout (location = 0) in vec3 position;
out vec4 color;

uniform float line_width;
uniform float line_stipple_factor;
uniform float line_stipple_pattern;


void main() {
float step = 1.0 / line_stipple_factor;
float pattern = mod(position.x * step, line_stipple_pattern);
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Relying on the x-coordinate alone will surely break things for completely vertical lines, no?

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Yes, I see! I can add a second mod() function to check the modulo of the y-coordinate of the position vector with the line stipple pattern. So by changing the condition on line 14, it will allow stippling for vertical lines too.

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Well, I don't think even that will be enough! We have to think in terms of stippling along the vector of the line we're drawing, rather than a cardinal (screen) direction, otherwise our results won't be consistent.

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I think I’ve come up with a good way to do this using dot products, and by letting the shader take vertex position and texture coordinates as inputs, while outputting the fragment texture coordinates. I'll send you my idea as a commit once I run some tests.

if (pattern > 0.5) {
discard;
}
gl_Position = vec4(position, 1.0);
color = vec4(1.0, 0.0, 0.0, 1.0);
}

// Compile the shader
GLuint shader = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(shader,1, &shader_source, NULL);
glCompileShader(shader);

// Bind the shader to the current OpenGl context
glUseProgram(shader);

// Set the uniforms
glUniform1f(glGetUniformLocation(shader, "line_width"), 1.0f);
glUniform1i(glGetUniformLocation(shader, "line_stipple_factor"), 1);
glUniform1ui(glGetUniformLocation(shader, "line_stipple_pattern"), 0xFFFF);

// Draw the line
glDrawArrays(GL_LINE_STRIP, 0, 4);