+ glBindTexture(GL_TEXTURE_2D, 0);
+ check_error();
+ glBindFramebuffer(GL_FRAMEBUFFER, 0);
+ check_error();
+ glDeleteFramebuffers(1, &fbo);
+ check_error();
+ glDeleteTextures(1, &dst_texnum);
+ check_error();
+ glDeleteTextures(1, &src_texnum);
+ check_error();
+
+ resource_pool.release_glsl_program(glsl_program_num);
+ glDeleteVertexArrays(1, &vao);
+ check_error();
+}
+
+void measure_roundoff_problems()
+{
+ ResourcePool resource_pool;
+
+ // Generate a destination texture to render to, and an FBO.
+ GLuint dst_texnum, fbo;
+
+ glGenTextures(1, &dst_texnum);
+ check_error();
+ glBindTexture(GL_TEXTURE_2D, dst_texnum);
+ check_error();
+ glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, 512, 1, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
+ check_error();
+
+ glGenFramebuffers(1, &fbo);
+ check_error();
+ glBindFramebuffer(GL_FRAMEBUFFER, fbo);
+ check_error();
+ glFramebufferTexture2D(
+ GL_FRAMEBUFFER,
+ GL_COLOR_ATTACHMENT0,
+ GL_TEXTURE_2D,
+ dst_texnum,
+ 0);
+ check_error();
+
+ // Now generate a texture where every value except the last should be
+ // rounded up to the next one. However, there are cards (in highly
+ // common use) that can't do this right, for unknown reasons.
+ GLuint src_texnum;
+ float texdata[512];
+ for (int i = 0; i < 256; ++i) {
+ texdata[i * 2 + 0] = (i + 0.48) / 255.0;
+ texdata[i * 2 + 1] = (i + 0.52) / 255.0;
+ }
+ glGenTextures(1, &src_texnum);
+ check_error();
+ glBindTexture(GL_TEXTURE_2D, src_texnum);
+ check_error();
+ glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
+ check_error();
+ glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
+ check_error();
+ glTexImage2D(GL_TEXTURE_2D, 0, GL_R32F, 512, 1, 0, GL_RED, GL_FLOAT, texdata);
+ check_error();
+
+ // Basic state.
+ glDisable(GL_BLEND);
+ check_error();
+ glDisable(GL_DEPTH_TEST);
+ check_error();
+ glDepthMask(GL_FALSE);
+ check_error();
+
+ glViewport(0, 0, 512, 1);
+
+ vector<string> frag_shader_outputs;
+ GLuint glsl_program_num = resource_pool.compile_glsl_program(
+ read_version_dependent_file("vs", "vert"),
+ read_version_dependent_file("texture1d", "frag"),
+ frag_shader_outputs);
+ glUseProgram(glsl_program_num);
+ check_error();
+ glUniform1i(glGetUniformLocation(glsl_program_num, "tex"), 0); // Bind the 2D sampler.
+
+ // Draw the texture stretched over a long quad, interpolating it out.
+ float vertices[] = {
+ 0.0f, 1.0f,
+ 0.0f, 0.0f,
+ 1.0f, 1.0f,
+ 1.0f, 0.0f
+ };
+
+ GLuint vao;
+ glGenVertexArrays(1, &vao);
+ check_error();
+ glBindVertexArray(vao);
+ check_error();
+
+ GLuint position_vbo = fill_vertex_attribute(glsl_program_num, "position", 2, GL_FLOAT, sizeof(vertices), vertices);
+ GLuint texcoord_vbo = fill_vertex_attribute(glsl_program_num, "texcoord", 2, GL_FLOAT, sizeof(vertices), vertices); // Same data.
+
+ glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
+ check_error();
+
+ cleanup_vertex_attribute(glsl_program_num, "position", position_vbo);
+ cleanup_vertex_attribute(glsl_program_num, "texcoord", texcoord_vbo);
+
+ glUseProgram(0);
+ check_error();
+
+ // Now read the data back and see what the card did. (Ignore the last value.)
+ // (We only look at the red channel; the others will surely be the same.)
+ unsigned char out_data[512 * 4];
+ glReadPixels(0, 0, 512, 1, GL_RGBA, GL_UNSIGNED_BYTE, out_data);
+ check_error();
+
+ int wrongly_rounded = 0;
+ for (unsigned i = 0; i < 255; ++i) {
+ if (out_data[(i * 2 + 0) * 4] != i) {
+ ++wrongly_rounded;
+ }
+ if (out_data[(i * 2 + 1) * 4] != i + 1) {
+ ++wrongly_rounded;
+ }
+ }
+
+ movit_num_wrongly_rounded = wrongly_rounded;
+
+ // Clean up.
+ glBindTexture(GL_TEXTURE_2D, 0);