Emulate glReadPixels of GL_ALPHA.

[movit] / init.cpp

diff --git a/init.cpp b/init.cpp
index 671c507c5588c7faf5783b7f0a500d1780fc9162..c5e81135dccb1de327883715f735a8e9506be41b 100644 (file)
--- a/init.cpp
+++ b/init.cpp
@@ -38,7 +38,7 @@ void measure_texel_subpixel_precision()
        check_error();
        glBindTexture(GL_TEXTURE_2D, dst_texnum);
        check_error();
-       glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA16F_ARB, width, 1, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
+       glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA16F, width, 1, 0, GL_RGBA, GL_FLOAT, NULL);
        check_error();
 
        glGenFramebuffers(1, &fbo);
@@ -122,14 +122,14 @@ void measure_texel_subpixel_precision()
        // Now read the data back and see what the card did.
        // (We only look at the red channel; the others will surely be the same.)
        // We assume a linear ramp; anything else will give sort of odd results here.
-       float out_data[width];
-       glReadPixels(0, 0, width, 1, GL_RED, GL_FLOAT, out_data);
+       float out_data[width * 4];
+       glReadPixels(0, 0, width, 1, GL_RGBA, GL_FLOAT, out_data);
        check_error();
 
        float biggest_jump = 0.0f;
        for (unsigned i = 1; i < width; ++i) {
-               assert(out_data[i] >= out_data[i - 1]);
-               biggest_jump = max(biggest_jump, out_data[i] - out_data[i - 1]);
+               assert(out_data[i * 4] >= out_data[(i - 1) * 4]);
+               biggest_jump = max(biggest_jump, out_data[i * 4] - out_data[(i - 1) * 4]);
        }
 
        assert(biggest_jump > 0.0);
@@ -242,16 +242,16 @@ void measure_roundoff_problems()
 
        // 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];
-       glReadPixels(0, 0, 512, 1, GL_RED, GL_UNSIGNED_BYTE, out_data);
+       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] != i) {
+               if (out_data[(i * 2 + 0) * 4] != i) {
                        ++wrongly_rounded;
                }
-               if (out_data[i * 2 + 1] != i + 1) {
+               if (out_data[(i * 2 + 1) * 4] != i + 1) {
                        ++wrongly_rounded;
                }
        }