GLSnow.cc

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#include "GLSnow.hh"
 
#include "GLContext.hh"
#include "gl_mat.hh"
#include "Display.hh"
#include "gl_vec.hh"
#include "openmsx.hh"
#include "random.hh"
 
using namespace gl;
 
namespace openmsx {
 
GLSnow::GLSnow(Display& display_)
        : Layer(Coverage::FULL, ZIndex::BACKGROUND)
        , display(display_)
        , noiseTexture(true, true) // enable interpolation + wrapping
{
        // Create noise texture.
        auto& generator = global_urng(); // fast (non-cryptographic) random numbers
        std::uniform_int_distribution distribution(0, 255);
        std::array<uint8_t, 128 * 128> buf;
        ranges::generate(buf, [&] { return distribution(generator); });
#if OPENGL_VERSION < OPENGL_3_3
        glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE, 128, 128, 0,
                     GL_LUMINANCE, GL_UNSIGNED_BYTE, buf.data());
#else
        // GL_LUMINANCE no longer supported in newer versions
        glTexImage2D(GL_TEXTURE_2D, 0, GL_RED, 128, 128, 0,
                     GL_RED, GL_UNSIGNED_BYTE, buf.data());
        GLint swizzleMask[] = {GL_RED, GL_RED, GL_RED, GL_ONE};
        glTexParameteriv(GL_TEXTURE_2D, GL_TEXTURE_SWIZZLE_RGBA, swizzleMask);
#endif
 
        static constexpr std::array pos = {
                std::array{vec2{-1, -1}, vec2{ 1, -1}, vec2{ 1,  1}, vec2{-1,  1}},
                std::array{vec2{-1,  1}, vec2{ 1,  1}, vec2{ 1, -1}, vec2{-1, -1}},
                std::array{vec2{-1,  1}, vec2{-1, -1}, vec2{ 1, -1}, vec2{ 1,  1}},
                std::array{vec2{ 1,  1}, vec2{ 1, -1}, vec2{-1, -1}, vec2{-1,  1}},
                std::array{vec2{ 1,  1}, vec2{-1,  1}, vec2{-1, -1}, vec2{ 1, -1}},
                std::array{vec2{ 1, -1}, vec2{-1, -1}, vec2{-1,  1}, vec2{ 1,  1}},
                std::array{vec2{ 1, -1}, vec2{ 1,  1}, vec2{-1,  1}, vec2{-1, -1}},
                std::array{vec2{-1, -1}, vec2{-1,  1}, vec2{ 1,  1}, vec2{ 1, -1}},
        };
        glBindBuffer(GL_ARRAY_BUFFER, vbo[0].get());
        glBufferData(GL_ARRAY_BUFFER, sizeof(pos), pos.data(), GL_STATIC_DRAW);
        glBindBuffer(GL_ARRAY_BUFFER, 0);
}
 
void GLSnow::paint(OutputSurface& /*output*/)
{
        // Rotate and mirror noise texture in consecutive frames to avoid
        // seeing 'patterns' in the noise.
        static unsigned cnt = 0;
        cnt = (cnt + 1) % 8;
 
        vec2 offset(random_float(0.0f, 1.0f), random_float(0.0f, 1.0f));
        const std::array tex = {
                offset + vec2(0.0f, 2.0f),
                offset + vec2(2.0f, 2.0f),
                offset + vec2(2.0f, 0.0f),
                offset + vec2(0.0f, 0.0f),
        };
 
        const auto& glContext = *gl::context;
        glContext.progTex.activate();
        glUniform4f(glContext.unifTexColor, 1.0f, 1.0f, 1.0f, 1.0f);
        mat4 I;
        glUniformMatrix4fv(glContext.unifTexMvp, 1, GL_FALSE, I.data());
 
        glBindBuffer(GL_ARRAY_BUFFER, vbo[0].get());
        const vec2* base = nullptr;
        glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 0, base + 4 * cnt);
        glEnableVertexAttribArray(0);
 
        glBindBuffer(GL_ARRAY_BUFFER, vbo[1].get());
        glBufferData(GL_ARRAY_BUFFER, sizeof(tex), tex.data(), GL_STREAM_DRAW);
        glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 0, nullptr);
        glEnableVertexAttribArray(1);
 
        noiseTexture.bind();
        glDrawArrays(GL_TRIANGLE_FAN, 0, 4);
        glDisableVertexAttribArray(1);
        glDisableVertexAttribArray(0);
        glBindBuffer(GL_ARRAY_BUFFER, 0);
 
        display.repaintDelayed(100 * 1000); // 10fps
}
 
} // namespace openmsx