I tried the following with SFML and it works perfectly fine! But I can't figure out what my problem is.
I'm trying to render a checkerboard in OpenGL but I get and incorrect output.
I tried to narrow down the problem and I notices that when I try to draw a 11 by 11 grid i get only 10 pixels in vertical direction
The texture itself is OK. I suspect problem is with vertex coordinates. Here's the code:
texture creation:
const int size = 11;
unsigned char buffer[size * size * 4];
for (size_t i = 0; i < size; i++)
{
for (size_t j = 0; j < size; j++)
{
unsigned char rgb = i % 2 == 1 || j % 2 == 1 ? 255 : 0;
int index = (i * size + j) * 4;
buffer[index] = rgb;
buffer[index + 1] = rgb;
buffer[index + 2] = rgb;
buffer[index + 3] = 255;
}
}
texture parameters:
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, pixels);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
vertices: (screen size is 1024 * 768, I'm drawing without any transformations at top right quarter)
float w = size / 512.0f;
float h = size / 384.0f;
GLfloat vertices[] =
{
0.0f, h, 0.0f, 1.0f,
0.0f, 0.0f, 0.0f, 0.0f,
w, h, 1.0f, 1.0f,
w, 0.0f, 1.0f, 0.0f
};
int positionLocation = glGetAttribLocation(program.getId(), "a_position");
int textureLocation = glGetAttribLocation(program.getId(), "a_texCoord");
glEnableVertexAttribArray(positionLocation);
glVertexAttribPointer(positionLocation, 2, GL_FLOAT, GL_FALSE, 4 * sizeof(float), vertices);
glEnableVertexAttribArray(textureLocation);
glVertexAttribPointer(textureLocation, 2, GL_FLOAT, GL_FALSE, 4 * sizeof(float), vertices + 2);
glUniform1i(textureLocation, 0);
drawing:
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
and the shaders:
const char* VertexShaderCode =
"attribute vec4 a_position; \n"
"attribute vec2 a_texCoord; \n"
"varying vec2 v_texCoord; \n"
"void main() \n"
"{ \n"
" gl_Position = a_position; \n"
" v_texCoord = a_texCoord; \n"
"}";
const char* FragmentShaderCode =
"uniform sampler2D s_texture; \n"
"varying vec2 v_texCoord; \n"
"void main() \n"
"{ \n"
" gl_FragColor = texture2D(s_texture, v_texCoord); \n"
"}";
