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@paulhoux
Last active May 14, 2016 20:25
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Semi-Circle Example (with shader).
#include "cinder/app/App.h"
#include "cinder/app/RendererGl.h"
#include "cinder/gl/gl.h"
using namespace ci;
using namespace ci::app;
using namespace std;
class YourApp : public App {
public:
void setup() override;
void draw() override;
private:
// A batch combines a mesh with a shader, and that's all we need to draw something.
gl::BatchRef mBatch;
};
void YourApp::setup()
{
// Create a rectangle mesh. Try making it bigger to see how the circle remains sharp (no pixelation).
auto mesh = gl::VboMesh::create( geom::Rect( { -128, -128, 128, 128 } ) ); // x1, y1, x2, y2
// Create our shader. Instead of having the source in this C++ file,
// we could also have chosen to load text files from the assets folder.
gl::GlslProg::Format fmt;
fmt.version( 150 );
fmt.vertex(
"uniform mat4 ciModelViewProjection;\n" // Cinder will pass this matrix to the shader for us.
""
"in vec4 ciPosition;\n" // Cinder will pass the mesh vertices to the shader for us.
"in vec2 ciTexCoord0;\n" // Cinder will pass the mesh texture coordinates to the shader for us.
"in vec4 ciColor;\n" // Cinder will pass the vertex colors to the shader for us.
""
"out vec2 vertTexCoord0;\n" // Our vertex shader will pass texture coordinates to the fragment shader.
"out vec4 vertColor;\n" // Our vertex shader will pass vertex colors to the fragment shader.
""
"void main( void )\n"
"{\n"
" vertTexCoord0 = ciTexCoord0;\n"
" vertColor = ciColor;\n"
""
" gl_Position = ciModelViewProjection * ciPosition;\n" // Required by OpenGL: it's the task of the vertex shader to convert from object to clip space.
"}" );
fmt.fragment(
"const float kInvPi = 1.0 / 3.14159265;\n"
// Play with the following values to see their effect.
"const float kBluriness = 1.0;\n"
"const float kRadius = 0.75;\n"
"const float kThickness = 0.2;\n"
"const float kArc = 0.5;\n"
"const float kOffset = 0.25;\n"
"in vec2 vertTexCoord0;\n" // Passed to us from the vertex shader and interpolated for this fragment (pixel).
"in vec4 vertColor;\n" // Passed to us from the vertex shader and interpolated for this fragment (pixel).
"out vec4 fragColor;\n" // The output of our fragment shader is a color for this fragment (pixel).
"void main( void )\n"
"{\n"
// Convert texture coordinates from range [0,1] to [-1,1]
" vec2 uv = 2.0 * vertTexCoord0 - 1.0;\n"
// Calculate distance to (0,0).
" float d = length( uv );\n"
// Calculate angle, so we can draw segments, too.
" float angle = atan( uv.x, uv.y ) * kInvPi * 0.5;\n"
" angle = fract( angle - kOffset );\n"
// Create an anti-aliased circle.
" float w = kBluriness * fwidth( d );\n"
" float circle = smoothstep( kRadius + w, kRadius - w, d );\n"
// Optionally, you could create a hole in it:
" float inner = kRadius - kThickness;\n"
" circle -= smoothstep( inner + w, inner - w, d );\n"
// Or only draw a portion (segment) of the circle.
" float segment = step( angle, kArc );\n"
" segment *= step( 0.0, angle );\n"
" circle *= mix( segment, 1.0, step( 1.0, kArc ) );\n"
// Output final color.
" fragColor.a = vertColor.a * circle;\n"
" fragColor.rgb = vertColor.rgb * fragColor.a;\n"
"}" );
auto glsl = gl::GlslProg::create( fmt );
mBatch = gl::Batch::create( mesh, glsl );
}
void YourApp::draw()
{
gl::clear();
gl::ScopedColor scpColor( 1.0f, 0.4f, 0.1f ); // Set color to orange.
gl::ScopedBlendPremult scpBlend; // Enable premultiplied alpha blending.
gl::ScopedModelMatrix scpModel; // Allows us to restore transformations after we're done.
gl::translate( getWindowSize() / 2 ); // Try disabling this line to see what it does.
mBatch->draw(); // Draw our mesh with the supplied shader.
gl::drawStrokedRect( { -128, -128, 128, 128 } ); // Draws the border of our rectangle.
}
CINDER_APP( YourApp, RendererGl )
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